Using ETRN to Retrieve Mail on a Dial-up Connection.

There are several cases where you or your customer may want to manually retrieve mail from another mail server:

If your IMail Server is set up as an SMTP mail gateway or as a backup server for another mail server, then IMail Server stores mail for that domain until the other server is online, or, until the Tries before Return To Sender setting has elapsed. The administrator of the other server can retrieve mail manually at any time.
If your IMail Server dials in to an ISP's mail server, then the ISP's server stores mail for you. You can retrieve it manually at any time.

To retrieve mail manually:

Use a Telnet program to connect to port 25 (the SMTP port) on the other mail server, and then issue the ETRN command for their domain. For example:

ETRN @domain2.com

ETRN mail.domain2.com

The first command retrieves all queued mail for the domain. The second command retrieves all queued mail for the mail host.