Hi all, my task is to retrieve a set of messages from GMail via POP3 (no IMAP). I can do RETR MSG #, and it is prohibited to delete.
Fetchmail and procmail are constantly trying to download a same set of new, unread messages (this part goes to ServerFault). Is there a header specially designed to distinguish previously read messages? Or I should do checksum of message body/subject/date?
The POP3 protocol doesn't support a read/seen sort of flag. Some servers support a non-standard header like X-Seen which acts like a read flag, you'll have to use the TOP to get a message's headers and see if it's been set (well more to determine if it's even there).
It's supposed to be up to the client to cover read flags in POP3, but the good news is you don't need to do a checksum, just use the UIDL which will give you a list of non-changing, unique IDs for the messages in the inbox, or if called with a message # will give you the unique ID for the message in that position in the mailbox (since you can't guarantee message position in the mailbox if other client's are accessing and may be deleting).