I learnt something new today!

I was wondering why when using TLS/SSL for secure POP3 Email, you still connect on port 110 instead of the POP3S port 995.

Well it seems there are two methods for secure POP3:

  1. Implicit TLS – connect to port 995 using TLS, the whole stream is encrypted.

  2. Explicit TLS – connect to port 110 in plaintext, then issue a ‘STARTTLS' command, and the stream is encrypted from there on.