I'm writing a small email parsing program using IMAP. When I first connect to my mail server I get UIDNEXT and HIGHESTMODSEQ, then go into IDLE and wait for new changes. After I get an Idle message I do a search and fetch all messages with a higher MODSEQ than MODSEQHIGHEST and UID greater than or equal to UIDNEXT. My question is how do I update these values after my fetches. Do I need to query the server for UIDNEXT and HIGHESTMODSEQ again? I know search returns the highest MODSEQ of the messages from my serch and I can get the highest UID of my messages returned by search, but is UIDNEXT always just my current highest UID+1?
I tried just fetching messages with MODSEQ greater than the MODSEQ value returned by my search but this results in me seeing messages I've already processed in subsequent searches.
UIDNEXT doesn't strictly have be one larger than the largest UID you've seen, but searching for the uid+1 necessarily produces the same results.
Suppose you've fetched UID 1000 and want the next larger. If the server skips 1001, searching for 1001:* and 1002:* must produce the same result, see?
It sounds as if you can skip MODSEQ in your case. MODSEQ is incremented when someone e.g. sets/clears the seen flag on a message. If you want to keep a cache updated the up-to-date seenness, you need to use MODSEQ. In your case it sounds as if you just want to process new messages: UID is all you need.