A mail fetcher is a software that retrieves mail from one or more POP3 mailboxes and sends it to another mailbox. Gmail includes a mail fetcher, but this new feature is not yet available for everyone.
"Gmail allows you to fetch mail from any of your other, non-Gmail accounts. You'll be able to read email from up to 5 additional accounts, all in one place, and take advantage of all of Gmail's great features."
A new mail account will create a label with the same name, so all mail received from that account will have an easy-to-remember label. If you don't like that, you can change the label.
You can choose to leave a copy of retrieved messages on the server, use a secure connection (SSL) when fetching mail and automatically archive new mail.
The feature should be available in Settings / Accounts. If you have it, some screenshots would be appreciated.
{ Via Digg. }
Update: Don't confuse this with other Gmail features: POP3 access (retrieve your Gmail messages with a client that supports POP3) and customization of the From address (send mail from a different address). Also, it's worth noting that Yahoo Mail has this feature.