Determines whether the email address is a real address.

Determines whether the email address is a real address.

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: 
 
  " );             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;     }}