如何准确判断邮件地址是否存在

if(sendHtmlMail_(mail)){    return true;    } else{    int i = 0;    //包含群组邮件，失败不重发    boolean isNeedRe = isNeedRe(mail);    while(!sendHtmlMail_(mail) && isNeedRe && i < 10){    try {    i++;    Thread.sleep(1000*60);    } catch (InterruptedException e) {    LOGGER.error("resend mail error", e);    }    }    return true;    }

import java.io.*;import java.net.*;import java.util.*;import javax.naming.*;import javax.naming.directory.*; public class SMTPMXLookup {  private static int hear( BufferedReader in ) throws IOException {   String line = null;   int res = 0;    while ( (line = in.readLine()) != null ) {     String pfx = line.substring( 0, 3 );     try {      res = Integer.parseInt( pfx );     }     catch (Exception ex) {      res = -1;     }     if ( line.charAt( 3 ) != '-' ) break;   }    return res;   }   private static void say( BufferedWriter wr, String text )   throws IOException {   wr.write( text + "/r/n" );   wr.flush();    return;   }   private static ArrayList getMX( String hostName )     throws NamingException {   // Perform a DNS lookup for MX records in the domain   Hashtable env = new Hashtable();   env.put("java.naming.factory.initial",       "com.sun.jndi.dns.DnsContextFactory");   DirContext ictx = new InitialDirContext( env );   Attributes attrs = ictx.getAttributes              ( hostName, new String[] { "MX" });   Attribute attr = attrs.get( "MX" );    // if we don't have an MX record, try the machine itself   if (( attr == null ) || ( attr.size() == 0 )) {    attrs = ictx.getAttributes( hostName, new String[] { "A" });    attr = attrs.get( "A" );    if( attr == null )      throw new NamingException           ( "No match for name '" + hostName + "'" );   }     // Huzzah! we have machines to try. Return them as an array list   // NOTE: We SHOULD take the preference into account to be absolutely   //  correct. This is left as an exercise for anyone who cares.   ArrayList res = new ArrayList();   NamingEnumeration en = attr.getAll();    while ( en.hasMore() ) {    String mailhost;    String x = (String) en.next();    String f[] = x.split( " " );    // THE fix *************    if (f.length == 1)      mailhost = f[0];    else if ( f[1].endsWith( "." ) )      mailhost = f[1].substring( 0, (f[1].length() - 1));    else      mailhost = f[1];    // THE fix *************          res.add( mailhost );   }   return res;   }   public static boolean isAddressValid( String address ) {   // Find the separator for the domain name   int pos = address.indexOf( '@' );    // If the address does not contain an '@', it's not valid   if ( pos == -1 ) return false;    // Isolate the domain/machine name and get a list of mail exchangers   String domain = address.substring( ++pos );   ArrayList mxList = null;   try {    mxList = getMX( domain );   }   catch (NamingException ex) {    return false;   }    // Just because we can send mail to the domain, doesn't mean that the   // address is valid, but if we can't, it's a sure sign that it isn't   if ( mxList.size() == 0 ) return false;    // Now, do the SMTP validation, try each mail exchanger until we get   // a positive acceptance. It *MAY* be possible for one MX to allow   // a message [store and forwarder for example] and another [like   // the actual mail server] to reject it. This is why we REALLY ought   // to take the preference into account.   for ( int mx = 0 ; mx < mxList.size() ; mx++ ) {     boolean valid = false;     try {       int res;       //       Socket skt = new Socket( (String) mxList.get( mx ), 25 );       BufferedReader rdr = new BufferedReader        ( new InputStreamReader( skt.getInputStream() ) );       BufferedWriter wtr = new BufferedWriter        ( new OutputStreamWriter( skt.getOutputStream() ) );        res = hear( rdr );       if ( res != 220 ) throw new Exception( "Invalid header" );       say( wtr, "EHLO rgagnon.com" );        res = hear( rdr );       if ( res != 250 ) throw new Exception( "Not ESMTP" );        // validate the sender address              say( wtr, "MAIL FROM: <tim@orbaker.com>" );       res = hear( rdr );       if ( res != 250 ) throw new Exception( "Sender rejected" );        say( wtr, "RCPT TO: <" + address + ">" );       res = hear( rdr );        // be polite       say( wtr, "RSET" ); hear( rdr );       say( wtr, "QUIT" ); hear( rdr );       if ( res != 250 )        throw new Exception( "Address is not valid!" );        valid = true;       rdr.close();       wtr.close();       skt.close();     }     catch (Exception ex) {      // Do nothing but try next host      ex.printStackTrace();     }     finally {      if ( valid ) return true;     }   }   return false;   }   public static void main( String args[] ) {   String testData[] = {     "real@rgagnon.com",     "you@acquisto.net",     "fail.me@nowhere.spam", // Invalid domain name     "arkham@bigmeanogre.net", // Invalid address     "nosuchaddress@yahoo.com" // Failure of this method     };    for ( int ctr = 0 ; ctr < testData.length ; ctr++ ) {    System.out.println( testData[ ctr ] + " is valid? " +       isAddressValid( testData[ ctr ] ) );   }   return;   }}

private static String[] removeInvalidateAddress(String[] addresses, String mailFrom)   {       ArrayList<String> validateAddresses = new ArrayList<String>();     String normalAddress = null;     int code;           SMTPTransport smptTrans = null;     if(StringUtils.isEmpty(mailFrom) || null == addresses)     {       return new String[0];     }     String sendCmd = "MAIL FROM:" + normalizeAddress(mailFrom);     try     {     smptTrans = (SMTPTransport)sendSession.getTransport("smtp");     smptTrans.connect();     code = smptTrans.simpleCommand(sendCmd);     if(code != 250 && code != 251)     {       logger.error("send from invalidate" + mailFrom);     }     else     {       for(String address : addresses)       {         normalAddress = normalizeAddress(address);         String cmd = "RCPT TO:" + normalAddress;     code = smptTrans.simpleCommand(cmd);     if(code == 250 || code == 251)     {       validateAddresses.add(address);     }       }     }     }     catch(MessagingException e)     {       logger.error("Validate mail address error. send from " + mailFrom, e);     }           String[] result = validateAddresses.toArray(new String[validateAddresses.size()]);     return result;   }       private static String normalizeAddress(String addr)    {     if ((!addr.startsWith("<")) && (!addr.endsWith(">")))       return "<" + addr + ">";     else       return addr;   }