SMTP (ETRN)

This service is useful to business customers running their own mail servers (eg Microsoft Exchange Server). It provides you with a dialup account, including a static IP Address, with incoming and outgoing mail via SMTP.

Instead of splitting incoming mail into POP3 mailboxes, it is stored on our SMTP server, and delivered to you on receipt of an ETRN prompt from your own SMTP server. The cost of the service is offset by the fact that you do not have to pay for individual POP3 mailboxes for each of your employees, and you gain complete control of all mail for your domain.

You can find a more detailed explanation of POP3 and SMTP email here.