fetchmailrc option 'uidl' does not work

[MartinSH]

my fechmailrc looks like this:

set daemon 300
set syslog

set postmaster “postmaster”
set bouncemail
set no spambounce
set properties “”

poll sslin.de with proto POP3 auth password user ‘user1@domain.de’ there with password ‘PASSWORD’ is ‘user1@domain.de’ here nokeep ssl #UID=‘user1’

this works fine.

But when i change the option ‘nokeep’ to ‘keep’ he received known mails every time again.
So i found the option ‘uidl’ , but i dont know how to use it.

Is there an example for a ‘fetchmailrc’ with a working ‘uidl’ ?