10.1 Email Service Protocols

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.