This is a really good place to go for fetchmail needs.
http://www.catb.org/~esr/fetchmail/fetchmail-man.html#5
The following excerpt from the page linked above is quoted here.
It’s possible to specify more than one user per server (this is only likely to be useful when running fetchmail in daemon mode as root). The ‘user’ keyword leads off a user description, and every user specification in a multi-user entry must include it. Here’s an example:
poll pop.provider.net proto pop3 port 3111
user "jsmith" with pass "secret1" is "smith" here
user jones with pass "secret2" is "jjones" here keep
This associates the local username ‘smith’ with the pop.provider.net username ‘jsmith’ and the local username ‘jjones’ with the pop.provider.net username ‘jones’. Mail for ‘jones’ is kept on the server after download.