How to only download the new mail when we keep the mail backup at mail IMAP server? Now it will download all the mail every time.
We can compare the uid, but it is so slow when the mail number is big.
Use Imap.Search, Expression.UID and Range.From.
This way you search only for required (new) uids on the IMAP server, and you download email data just for new emails.
You can find more details here: Get new emails using IMAP