Here are the common network ports used for email delivery and collection through SMTP, POP-2, POP-3, and IMAP:
smtp 25/tcp pop2 109/tcp pop3 110/tcp imap2 143/tcp
SSL-enhanced versions of these services exist and are found running on the following ports:
ssmtp 465/tcp imaps 993/tcp pop3s 995/tcp
You can use stunnel and standard plaintext assessment tools to test SSL-enhanced services (see Chapter 6). For example, the stunnel tool negotiates and maintains the SSL connection, allowing for plaintext access to the underlying protocol.