src/org/ibex/mail/SMTP.java

   1 // Copyright 2000-2005 the Contributors, as shown in the revision logs.
   2 // Licensed under the Apache Public Source License 2.0 ("the License").
   3 // You may not use this file except in compliance with the License.
   4
   5 package org.ibex.mail;
   6 import org.ibex.mail.target.*;
   7 import org.ibex.util.*;
   8 import org.ibex.net.*;
   9 import org.ibex.io.*;
  10 import java.net.*;
  11 import java.io.*;
  12 import java.util.*;
  13 import java.text.*;
  14 import javax.naming.*;
  15 import javax.naming.directory.*;
  16
  17 // FIXME: inbound throttling/ratelimiting
  18
  19 // "Address enumeration detection" -- notice when it looks like somebody
  20 // is trying a raft of addresses.
  21
  22 // RFC's implemented
  23 // RFC2554: SMTP Service Extension for Authentication
  24 //     - did not implement section 5, though
  25 // RFC4616: SASL PLAIN
  26
  27 // Note: we can't actually use status codes for feedback if we accept
  28 // multiple destination addresses...  a failure on one and success on
  29 // the other...
  30
  31 // FIXME: logging: current logging sucks
  32 // FIXME: loop prevention
  33 // FIXME: probably need some throttling on outbound mail
  34
  35 // FEATURE: public static boolean validate(Address a)
  36 // FEATURE: rate-limiting
  37
  38 // FEATURE: infer messageid, date, if not present (?)
  39 // FEATURE: exponential backoff on retry time?
  40 // FEATURE: RFC2822, section 4.5.1: special "postmaster" address
  41 // FEATURE: RFC2822, section 4.5.4.1: retry strategies
  42 // FEATURE: RFC2822, section 5, multiple MX records, preferences, ordering
  43 // FEATURE: RFC2822, end of 4.1.2: backslashes in headers
  44 public class SMTP {
  45
  46     public static final SimpleDateFormat dateFormat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
  47     public static final int numOutgoingThreads = 5;
  48
  49     public static final int GRAYLIST_MINWAIT =  1000 * 60 * 60;           // one hour
  50     public static final int GRAYLIST_MAXWAIT =  1000 * 60 * 60 * 24 * 5;  // five days
  51
  52     public static final Graylist graylist;
  53     public static final Whitelist whitelist;
  54     static {
  55         try {
  56             graylist =  new Graylist(Mailbox.STORAGE_ROOT+"/db/graylist.sqlite");
  57             whitelist = new Whitelist(Mailbox.STORAGE_ROOT+"/db/whitelist.sqlite");
  58         } catch (Exception e) {
  59             throw new RuntimeException(e);
  60         }
  61     }
  62
  63     public static final int MAX_MESSAGE_SIZE =
  64         Integer.parseInt(System.getProperty("org.ibex.mail.smtp.maxMessageSize", "-1"));
  65
  66     private static final Mailbox spool =
  67         FileBasedMailbox.getFileBasedMailbox(Mailbox.STORAGE_ROOT,false).slash("spool",true).slash("smtp",true).getMailbox();
  68
  69     static {
  70         for(int i=0; i<numOutgoingThreads; i++)
  71             new Outgoing().start();
  72     }
  73
  74     public static void enqueue(Message m) throws IOException {
  75         if (!m.envelopeTo.isLocal()) Outgoing.enqueue(m);
  76         else                         Target.root.accept(m);
  77     }
  78
  79     public static class SMTPException extends MailException {
  80         int code;
  81         String message;
  82         public SMTPException(String s) {
  83             try {
  84                 code = Integer.parseInt(s.substring(0, s.indexOf(' ')));
  85                 message = s.substring(s.indexOf(' ')+1);
  86             } catch (NumberFormatException nfe) {
  87                 code = -1;
  88                 message = s;
  89             }
  90         }
  91         public String toString() { return "SMTP " + code + ": " + message; }
  92         public String getMessage() { return toString(); }
  93     }
  94
  95     // Server //////////////////////////////////////////////////////////////////////////////
  96
  97     public static class Server {
  98         public void handleRequest(Connection conn) throws IOException {
  99             conn.setTimeout(5 * 60 * 1000);
 100             conn.setNewline("\r\n");
 101             conn.println("220 " + conn.vhost + " ESMTP " + this.getClass().getName());
 102             Address from = null;
 103             Vector to = new Vector();
 104             boolean ehlo = false;
 105             String remotehost = null;
 106             String authenticatedAs = null;
 107             int failedRcptCount = 0;
 108             for(String command = conn.readln(); ; command = conn.readln()) try {
 109                 if (command == null) return;
 110                 Log.warn("**"+conn.getRemoteAddress()+"**", command);
 111                 String c = command.toUpperCase();
 112                 if (c.startsWith("HELO"))        {
 113                     remotehost = c.substring(5).trim();
 114                     conn.println("250 HELO " + conn.vhost);
 115                     from = null; to = new Vector();
 116                 } else if (c.startsWith("EHLO")) {
 117                     remotehost = c.substring(5).trim();
 118                     conn.println("250-"+conn.vhost);
 119                     //conn.println("250-AUTH");
 120                     conn.println("250-AUTH PLAIN");
 121                     //conn.println("250-STARTTLS");
 122                     conn.println("250 HELP");
 123                     ehlo = true;
 124                     from = null; to = new Vector();
 125                 } else if (c.startsWith("RSET")) { conn.println("250 reset ok");           from = null; to = new Vector();
 126                 } else if (c.startsWith("HELP")) { conn.println("214 you are beyond help.  see a trained professional.");
 127                 } else if (c.startsWith("VRFY")) { conn.println("502 VRFY not supported");
 128                 } else if (c.startsWith("EXPN")) { conn.println("502 EXPN not supported");
 129                 } else if (c.startsWith("NOOP")) { conn.println("250 OK");
 130                 } else if (c.startsWith("QUIT")) { conn.println("221 " + conn.vhost + " closing connection"); return;
 131                 } else if (c.startsWith("STARTTLS")) {
 132                     conn.println("220 starting TLS...");
 133                     conn.flush();
 134                     conn = conn.negotiateSSL(true);
 135                     from = null; to = new Vector();
 136                 } else if (c.startsWith("AUTH")) {
 137                     if (authenticatedAs != null) {
 138                         conn.println("503 you are already authenticated; you must reconnect to reauth");
 139                     } else {
 140                         String mechanism = command.substring(4).trim();
 141                         String rest = "";
 142                         if (mechanism.indexOf(' ')!=-1) {
 143                             rest      = mechanism.substring(mechanism.indexOf(' ')+1).trim();
 144                             mechanism = mechanism.substring(0, mechanism.indexOf(' '));
 145                         }
 146                         if (mechanism.equals("PLAIN")) {
 147                             // 538 Encryption required for requested authentication mechanism?
 148                             byte[] bytes = Encode.fromBase64(rest);
 149                             String authenticateUser = null;
 150                             String authorizeUser = null;
 151                             String password = null;
 152                             int start = 0;
 153                             for(int i=0; i<=bytes.length; i++) {
 154                                 if (i<bytes.length && bytes[i]!=0) continue;
 155                                 String result = new String(bytes, start, i-start, "UTF-8");
 156                                 if (authenticateUser==null)   authenticateUser = result;
 157                                 else if (authorizeUser==null) authorizeUser = result;
 158                                 else if (password==null)      password = result;
 159                                 start = i+1;
 160                             }
 161                             // FIXME: be smarter here
 162                             if (Main.auth.login(authorizeUser, password)!=null)
 163                                 authenticatedAs = authenticateUser;
 164                             conn.println("235 Authentication successful");
 165                             /*
 166                         } else if (mechanism.equals("CRAM-MD5")) {
 167                             String challenge = ;
 168                             conn.println("334 "+challenge);
 169                             String resp = conn.readln();
 170                             if (resp.equals("*")) {
 171                                 conn.println("501 client requested AUTH cancellation");
 172                             }
 173                         } else if (mechanism.equals("ANONYMOUS")) {
 174                         } else if (mechanism.equals("EXTERNAL")) {
 175                         } else if (mechanism.equals("DIGEST-MD5")) {
 176                             */
 177                         } else {
 178                             conn.println("504 unrecognized authentication type");
 179                         }
 180                         // on success, reset to initial state; client will EHLO again
 181                         from = null; to = new Vector();
 182                     }
 183                 } else if (c.startsWith("MAIL FROM:")) {
 184                     command = command.substring(10).trim();
 185                     from = command.equals("<>") ? null : new Address(command);
 186                     conn.println("250 " + from + " is syntactically correct");
 187                     // FEATURE: perform SMTP validation on the address, reject if invalid
 188                 } else if (c.startsWith("RCPT TO:")) {
 189                     // some clients are broken and put RCPT first; we will tolerate this
 190                     command = command.substring(8).trim();
 191                     if(command.indexOf(' ') != -1) command = command.substring(0, command.indexOf(' '));
 192                     Address addr = new Address(command);
 193                     if (conn.getRemoteAddress().isLoopbackAddress() || (from!=null&&from.toString().indexOf("johnw")!=-1)) {
 194                         conn.println("250 you are connected locally, so I will let you send");
 195                         to.addElement(addr);
 196                         if (!whitelist.isWhitelisted(addr))
 197                             whitelist.addWhitelist(addr);
 198                     } else if (authenticatedAs!=null) {
 199                         conn.println("250 you are authenticated as "+authenticatedAs+", so I will let you send");
 200                         to.addElement(addr);
 201                         if (!whitelist.isWhitelisted(addr))
 202                             whitelist.addWhitelist(addr);
 203                     } else if (addr.isLocal()) {
 204                         if (to.size() > 3) {
 205                             conn.println("536 sorry, limit on 3 RCPT TO's per DATA");
 206                         } else {
 207                             // FEATURE: should check the address further and give 550 if undeliverable
 208                             conn.println("250 " + addr + " is on this machine; I will deliver it");
 209                             to.addElement(addr);
 210                         }
 211                     } else {
 212                         conn.println("535 sorry, " + addr + " is not on this machine, you are not connected from localhost, and I will not relay without SMTP AUTH");
 213                         Log.warn("","535 sorry, " + addr + " is not on this machine, you are not connected from localhost, and I will not relay without SMTP AUTH");
 214                         failedRcptCount++;
 215                         if (failedRcptCount > 3) {
 216                             conn.close();
 217                             return;
 218                         }
 219                     }
 220                     conn.flush();
 221                 } else if (c.startsWith("DATA")) {
 222                     //if (from == null) { conn.println("503 MAIL FROM command must precede DATA"); continue; }
 223                     if (to == null || to.size()==0) { conn.println("503 RCPT TO command must precede DATA"); continue; }
 224                     if (!graylist.isWhitelisted(conn.getRemoteAddress()) && !conn.getRemoteAddress().isLoopbackAddress() && authenticatedAs==null) {
 225                         long when = graylist.getGrayListTimestamp(conn.getRemoteAddress(), from+"", to+"");
 226                         if (when == 0 || System.currentTimeMillis() - when > GRAYLIST_MAXWAIT) {
 227                             graylist.setGrayListTimestamp(conn.getRemoteAddress(), from+"", to+"",  System.currentTimeMillis());
 228                             conn.println("451 you are graylisted; please try back in one hour to be whitelisted");
 229                             Log.warn(conn.getRemoteAddress().toString(), "451 you are graylisted; please try back in one hour to be whitelisted");
 230                             conn.flush();
 231                             continue;
 232                         } else if (System.currentTimeMillis() - when > GRAYLIST_MINWAIT) {
 233                             graylist.addWhitelist(conn.getRemoteAddress());
 234                             conn.println("354 (you have been whitelisted) Enter message, ending with \".\" on a line by itself");
 235                             Log.warn(conn.getRemoteAddress().toString(), "has been whitelisted");
 236                         } else {
 237                             conn.println("451 you are still graylisted (since "+new java.util.Date(when)+")");
 238                             conn.flush();
 239                             Log.warn(conn.getRemoteAddress().toString(), "451 you are still graylisted (since "+new java.util.Date(when)+")");
 240                             continue;
 241                         }
 242                     } else {
 243                         conn.println("354 Enter message, ending with \".\" on a line by itself");
 244                     }
 245                     conn.flush();
 246                     try {
 247                         // FIXME: deal with messages larger than memory here?
 248                         StringBuffer buf = new StringBuffer();
 249                         buf.append("Received: from " + conn.getRemoteHostname() + " (" + remotehost + ")\r\n");
 250                         buf.append("          by "+conn.vhost+" ("+SMTP.class.getName()+") with "+(ehlo?"ESMTP":"SMTP") + "\r\n");
 251                         buf.append("          for ");
 252                         // FIXME: this is leaking BCC addrs
 253                         // for(int i=0; i<to.size(); i++) buf.append(to.elementAt(i) + " ");
 254                         buf.append("; " + dateFormat.format(new Date()) + "\r\n");
 255
 256                         // FIXME: some sort of stream transformer here?
 257                         while(true) {
 258                             String s = conn.readln();
 259                             if (s == null) throw new RuntimeException("connection closed");
 260                             if (s.equals(".")) break;
 261                             if (s.startsWith(".")) s = s.substring(1);
 262                             buf.append(s + "\r\n");
 263                             if (MAX_MESSAGE_SIZE != -1 && buf.length() > MAX_MESSAGE_SIZE && (from+"").indexOf("paperless")==-1) {
 264                                 Log.error("**"+conn.getRemoteAddress()+"**",
 265                                           "sorry, this mail server only accepts messages of less than " +
 266                                           ByteSize.toString(MAX_MESSAGE_SIZE));
 267                                 throw new MailException.Malformed("sorry, this mail server only accepts messages of less than " +
 268                                                                   ByteSize.toString(MAX_MESSAGE_SIZE));
 269                             }
 270                         }
 271                         String message = buf.toString();
 272                         Message m = null;
 273                         for(int i=0; i<to.size(); i++)
 274                             enqueue(m = Message.newMessage(Fountain.Util.create(message)).withEnvelope(from, (Address)to.elementAt(i)));
 275                         if (m != null) Log.info(SMTP.class, "accepted message: " + m.summary());
 276                         conn.println("250 message accepted");
 277                         conn.flush();
 278                         from = null; to = new Vector();
 279                     } catch (MailException.Malformed mfe) {    conn.println("501 " + mfe.toString());
 280                     } catch (MailException.MailboxFull mbf) {  conn.println("452 " + mbf);
 281                     } catch (Script.Later.LaterException le) { conn.println("453 try again later");
 282                     } catch (Script.Reject.RejectException re) {
 283                         Log.warn(SMTP.class, "rejecting message due to: " + re.reason + "\n   " + re.m.summary());
 284                         conn.println("501 " + re.reason);
 285                     }
 286                 } else                    { conn.println("500 unrecognized command"); }
 287             } catch (Message.Malformed e) { conn.println("501 " + e.toString()); }
 288         }
 289     }
 290
 291
 292     // Outgoing Mail Thread //////////////////////////////////////////////////////////////////////////////
 293
 294     public static class Outgoing extends Thread {
 295
 296         private static final HashMap deadHosts = new HashMap();
 297         public static void enqueue(Message m) throws IOException {
 298             if (m == null) { Log.warn(Outgoing.class, "attempted to enqueue(null)"); return; }
 299             String traces = m.headers.get("Received");
 300             if (traces!=null) {
 301                 int lines = 0;
 302                 for(int i=0; i<traces.length(); i++)
 303                     if (traces.charAt(i)=='\n' || traces.charAt(i)=='\r')
 304                         lines++;
 305                 if (lines > 100) { // required by rfc
 306                     Log.warn(SMTP.Outgoing.class, "Message with " + lines + " trace hops; dropping\n" + m.summary());
 307                     return;
 308                 }
 309             }
 310             synchronized(Outgoing.class) {
 311                 spool.insert(m, Mailbox.Flag.defaultFlags);
 312                 Outgoing.class.notifyAll();
 313             }
 314         }
 315
 316         public static boolean attempt(Message m) throws IOException { return attempt(m, false); }
 317         public static boolean attempt(Message m, boolean noBounces) throws IOException {
 318             if (m.envelopeTo == null) {
 319                 Log.warn(SMTP.Outgoing.class, "aieeee, null envelopeTo: " + m.summary());
 320                 return false;
 321             }
 322             InetAddress[] mx = getMailExchangerIPs(m.envelopeTo.host);
 323             if (mx.length == 0) {
 324                 if (!noBounces) {
 325                     enqueue(m.bounce("could not resolve " + m.envelopeTo.host));
 326                     return true;
 327                 } else {
 328                     Log.warn(SMTP.Outgoing.class, "could not resolve " + m.envelopeTo.host);
 329                     return false;
 330                 }
 331             }
 332             if (new Date().getTime() - m.arrival.getTime() > 1000 * 60 * 60 * 24 * 5) {
 333                 if (!noBounces) {
 334                     enqueue(m.bounce("could not send for 5 days"));
 335                     return true;
 336                 } else {
 337                     Log.warn(SMTP.Outgoing.class, "could not send for 5 days: " + m.summary());
 338                     return false;
 339                 }
 340             }
 341             for(int i=0; i<mx.length; i++) {
 342                 //if (deadHosts.contains(mx[i])) continue;
 343                 if (attempt(m, mx[i])) return true;
 344             }
 345             return false;
 346         }
 347
 348         private static void check(String s, Connection conn) {
 349             if (s==null) return;
 350             while (s.length() > 3 && s.charAt(3) == '-') s = conn.readln();
 351             //if (s.startsWith("4")||s.startsWith("5")) throw new SMTPException(s);
 352             if (!s.startsWith("2")&&!s.startsWith("3")) throw new SMTPException(s);
 353         }
 354         private static boolean attempt(final Message m, final InetAddress mx) {
 355             boolean accepted = false;
 356             Connection conn = null;
 357             try {
 358                 conn = new Connection(new Socket(mx, 25), InetAddress.getLocalHost().getHostName());
 359                 conn.setNewline("\r\n");
 360                 conn.setTimeout(60 * 1000);
 361                 check(conn.readln(), conn);  // banner
 362                 try {
 363                     conn.println("EHLO " + conn.vhost);
 364                     check(conn.readln(), conn);
 365                 } catch (SMTPException smtpe) {
 366                     conn.println("HELO " + conn.vhost);
 367                     check(conn.readln(), conn);
 368                 }
 369                 String envelopeFrom = m.envelopeFrom==null ? "" : m.envelopeFrom.toString();
 370                 conn.println("MAIL FROM:<" + envelopeFrom +">");            check(conn.readln(), conn);
 371                 conn.println("RCPT TO:<"   + m.envelopeTo.toString()+">");  check(conn.readln(), conn);
 372                 conn.println("DATA");                                       check(conn.readln(), conn);
 373
 374                 Headers head = new Headers(m.headers,
 375                                            new String[] {
 376                                                "return-path", null,
 377                                                "bcc", null
 378                                            });
 379                 Stream stream = head.getStream();
 380                 for(String s = stream.readln(); s!=null; s=stream.readln()) {
 381                     if (s.startsWith(".")) conn.print(".");
 382                     conn.println(s);
 383                 }
 384                 conn.println("");
 385                 stream = m.getBody().getStream();
 386                 for(String s = stream.readln(); s!=null; s=stream.readln()) {
 387                     if (s.startsWith(".")) conn.print(".");
 388                     conn.println(s);
 389                 }
 390                 conn.println(".");
 391                 String resp = conn.readln();
 392                 if (resp == null)
 393                     throw new SMTPException("server " + mx + " closed connection without accepting message");
 394                 check(resp, conn);
 395                 Log.warn(SMTP.Outgoing.class, "success: " + mx + " accepted " + m.summary() + "\n["+resp+"]");
 396                 accepted = true;
 397                 conn.close();
 398             } catch (SMTPException e) {
 399                 if (accepted) return true;
 400                 Log.warn(SMTP.Outgoing.class, "    unable to send; error=" + e);
 401                 Log.warn(SMTP.Outgoing.class, "      message: " + m.summary());
 402                 Log.warn(SMTP.Outgoing.class, e);
 403                 /*
 404                   // FIXME: we should not be bouncing here!
 405                 if (e.code >= 500 && e.code <= 599) {
 406                     try {
 407                         attempt(m.bounce("unable to deliver: " + e), true);
 408                     } catch (Exception ex) {
 409                         Log.error(SMTP.Outgoing.class, "exception while trying to deliver bounce; giving up completely");
 410                         Log.error(SMTP.Outgoing.class, ex);
 411                     }
 412                     return true;
 413                 }
 414                 */
 415                 return false;
 416             } catch (Exception e) {
 417                 if (accepted) return true;
 418                 Log.warn(SMTP.Outgoing.class, "    unable to send; error=" + e);
 419                 Log.warn(SMTP.Outgoing.class, "      message: " + m.summary());
 420                 Log.warn(SMTP.Outgoing.class, e);
 421                 //if (conn != null) Log.warn(SMTP.Outgoing.class, conn.dumpLog());
 422                 return false;
 423             } finally {
 424                 if (conn != null) conn.close();
 425             }
 426             return accepted;
 427         }
 428
 429         private static HashSet<Outgoing> threads = new HashSet<Outgoing>();
 430         private static int serials = 1;
 431         private int serial = serials++;
 432         private Mailbox.Iterator it;
 433
 434         public Outgoing() {
 435             synchronized(Outgoing.class) {
 436                 threads.add(this);
 437             }
 438         }
 439
 440         public void wake() {
 441             int count = spool.count(Query.all());
 442             Log.info(SMTP.Outgoing.class, "outgoing thread #"+serial+" woke up; " + count + " messages to send");
 443             try {
 444                 while(true) {
 445                     boolean good = false;
 446                     synchronized(Outgoing.class) {
 447                         it = spool.iterator();
 448                         OUTER: for(; it.next(); ) {
 449                             for(Outgoing o : threads)
 450                                 if (o!=this && o.it != null && o.it.uid()==it.uid())
 451                                     continue OUTER;
 452                             good = true;
 453                             break;
 454                         }
 455                     }
 456                     if (!good) break;
 457                     try {
 458                         if (attempt(it.cur())) it.delete();
 459                     } catch (Exception e) {
 460                         Log.error(SMTP.Outgoing.class, e);
 461                     }
 462                     Log.info(this, "sleeping for 3s...");
 463                     Thread.sleep(3000);
 464                 }
 465             } catch (Exception e) {
 466                 //if (e instanceof InterruptedException) throw e;
 467                 Log.error(SMTP.Outgoing.class, e);
 468             }
 469             Log.info(SMTP.Outgoing.class, "outgoing thread #"+serial+" going back to sleep");
 470             it = null;
 471         }
 472
 473         public void run() {
 474             try {
 475                 while(true) {
 476                     Log.setThreadAnnotation("[outgoing #"+serial+"] ");
 477                     wake();
 478                     Thread.sleep(1000);
 479                     synchronized(Outgoing.class) {
 480                         Outgoing.class.wait(5 * 60 * 1000);
 481                     }
 482                 }
 483             } catch (InterruptedException e) { Log.warn(this, e); }
 484         }
 485     }
 486
 487     public static InetAddress[] getMailExchangerIPs(String hostName) {
 488         InetAddress[] ret;
 489         try {
 490             Hashtable env = new Hashtable();
 491             env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
 492             DirContext ictx = new InitialDirContext(env);
 493             Attributes attrs = ictx.getAttributes(hostName, new String[] { "MX" });
 494             Attribute attr = attrs.get("MX");
 495             if (attr == null) {
 496                 ret = new InetAddress[1];
 497                 try {
 498                     ret[0] = InetAddress.getByName(hostName);
 499                     if (ret[0].equals(IP.getIP(127,0,0,1)) || ret[0].isLoopbackAddress()) throw new UnknownHostException();
 500                     return ret;
 501                 } catch (UnknownHostException uhe) {
 502                     Log.warn(SMTP.class, "no MX hosts or A record for " + hostName);
 503                     return new InetAddress[0];
 504                 }
 505             } else {
 506                 ret = new InetAddress[attr.size()];
 507                 NamingEnumeration ne = attr.getAll();
 508                 for(int i=0; ne.hasMore();) {
 509                     String mx = (String)ne.next();
 510                     // FIXME we should be sorting here
 511                     mx = mx.substring(mx.indexOf(" ") + 1);
 512                     if (mx.charAt(mx.length() - 1) == '.') mx = mx.substring(0, mx.length() - 1);
 513                     InetAddress ia = InetAddress.getByName(mx);
 514                     if (ia.equals(IP.getIP(127,0,0,1)) || ia.isLoopbackAddress()) continue;
 515                     ret[i++] = ia;
 516                 }
 517             }
 518         } catch (Exception e) {
 519             Log.warn(SMTP.class, "couldn't find MX host for " + hostName + " due to");
 520             Log.warn(SMTP.class, e);
 521             return new InetAddress[0];
 522         }
 523         return ret;
 524     }
 525 }