Month: September 2017

According to fastmail.com ("SSL/TLS vs plaintext/STARTTLS port numbers" part) and thousands of other sources in the Internet (emphasis mine):

• IMAP uses port 143, but SSL/TLS encrypted IMAP uses port 993.
• POP uses port 110, but SSL/TLS encrypted POP uses port 995.
• SMTP uses port 25, but SSL/TLS encrypted SMTP uses port 465.

That doesn't count to morons who produced Microsoft Outlook 2010. They've decided that switching encryption method for IMAP between None to SSL will change port from 143 to 993 and back (correct!). While, doing exactly the same for SMTP won't change port at all.

This way Outlook is problably the only mail client in the world who is trying (unless you manually correct it) to establish secure, encrypted SMTP connection over port 25. An attempt which is doomed by its definition. Congrats again, Microsoft fucks!