On Wed, 2016-05-25 at 06:19 +1000, Stephen Morris wrote:
How do you configure Tbird for the way you use the mail service (different retention periods on folders and only downloading mail you are interested in), as relative to the retention period of mail on the remote server, the version of Tbird I am using appears to only provide 1 setting relative to retention on the server which I have set to 7 days, rather than as I used to have it set to, to delete when downloaded (Are you implementing it via folder level mail rules?). Experience also indicates that this setting doesn't work properly anyway (I haven't determined yet whether this failure was relative to imap or pop) as the mailbox at the isp's end retained mail that was significantly older than than the retention period threshold. I also ran into the issue when I switched to imap that for several days afterwards I got duplicate emails in my Tbird inbox. My isp's support guys were unable to explain why, and also not explain why it was the all the emails that were duplicated did not physically exist in their mailbox and emails for the same days that were not duplicated still existed in their mailbox.
I don't know why you're having this problem, but it has nothing to do with IMAP per se. IMAP has no concept of a retention period. Looks like your difficulties arise from something in your TBird configuration but as I use Evolution I couldn't say what it is.
poc