Using fetchmail is not a viable solution for archiving your mail. You should use something like
Zimbra Archive & Discovery or HSM within Zimbra or use the BCC option to archive all email to another server or even the Backup facility (if you use NE) to archive your mail offsite. What exactly are you trying to achieve? There are also several threads on this subject in the forums if you'd like to search and see what others are doing.
Please update your
forum profile with the output of the following command (do not post it in this thread):