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Which SMTP service port does a mail client usually connect to?

Is it the same for both SSL and Non-SSL?

Are there any common alternative?

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up vote 5 down vote accepted

The SMTP service uses port 25 by default. Secure SMTP (SSMTP uses SSL) uses port 465 by default. Although these are the defaults, pretty much every unused port number can be used. Most email clients will only try to connect to these ports unless instructed otherwise.

These are the default email service ports:

  • POP3: port 110
  • Secure POP3 (SSL-POP): port 995
  • IMAP: port 143
  • Secure IMAP (IMAPS): port 585
  • IMAP4 over SSL (IMAP4-SSL): port 993
  • SMTP: port 25
  • Secure SMTP (SSMTP): port 465
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I should probably add 587 as I just found out.. – xiamx Feb 2 '11 at 1:59
The non-ssl ports may support startTLS which will switch to SSL after connecting. This is replacing SSL only ports for a lot of services. Well known services such as SMTP, IMAP, and POP3 have assigned ports as listed above. The submission port 587 is intended for email submission but Message User Agents as opposed to mail exchange on port 25. Port 587 should support startTLS, and will usually require authentication. – BillThor Feb 2 '11 at 2:33

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