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Editorial Team
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Asked: 2026-06-01T22:43:43+00:00

I’m working on a project to auto-configure a user’s email server settings in Java.

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I’m working on a project to auto-configure a user’s email server settings in Java. I am extracting the mail server from his email address and looking up the MX records of that mail server using the DirContext class with com.sun.jndi.dns.DnsContextFactory.

Then I’m opening a Socket to each server and testing them using a HELO command and checking the responses.

My problem is that this works only when I test it with the unsecure SMTP port 25. How can I use it with the secure port 465?

I tried using Secure Sockets by using

SSLSocketFactory sslsocketfactory = (SSLSocketFactory)SSLSocketFactory.getDefault();
SSLSocket socket = (SSLSocket)sslsocketfactory.createSocket(mailserver, STANDARD_SMTP_PORT);

But all connections get a timeout exception as follows

alt1.gmail-smtp-in.l.google.com. java.net.ConnectException: Operation timed out

Please help.

Further Info: I am not creating a mail client. This is to simplify the mail server settings for an already existing mail client.

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1 Answer

  1. Editorial Team

    SMTP-SSL (Port 465) afaik is deprecated, so instead of trying to connect to a ssl socket you’d actually connect “plaintext” on port 25 (or 587 for smtp auth connections), but send EHLO instead of HELO and see if the server supports STARTTLS which replaces the deprecated SMTP-SSL. after the client sends the STARTTLS command, the connection is encrypted, so, port 25 is not per se “unsecure”

    telnet alt1.gmail-smtp-in.l.google.com 25
Trying 173.194.71.26...
Connected to alt1.gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP i7si4620651lbb.76
EHLO myserver.com
250-mx.google.com at your service, [x.x.x.x]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS                  <<--------- this is what you're looking for
250 ENHANCEDSTATUSCODES
STARTTLS      <<--- client command to actually start encrypting the traffic
220 2.0.0 Ready to start TLS
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