By default Dovecot generates POP3 UIDs differently than UW-IMAP, which causes
POP3 clients to not recognize them and redownload messages they had downloaded
If you want Dovecot to use the same UID format as UW-IMAP/ipop3d so that clients
can recognize them, your required action depends on the Dovecot version.
With Dovecot 0.99.x you'll have to patch Dovecot
Patch referenced in  is attached to this BZ.
Created attachment 138264 [details]
Patch to address issues with dovecot migration from IMAP to POP3. From http://dovecot.org/patches/old/pop3-uidl-uwimap.patch.
*** This bug has been marked as a duplicate of 210246 ***