I have Thunderbird 52.91.1 and recently (as of either 10/11/2018 or 10/12/2018) all my emails older than 14 days have been/are deleted. I run 2 accounts, both IMAP, and only the inbox folder is affected on each. My other folders still hold emails older than 14 days, including the sent folder. Every day it deletes anything that is older than the 14 days. I've removed all other instances of those accounts on other devices (phone and laptop) to be sure that those devices aren't deleting emails and then showing up as deleted on this computer. I have checked settings under both the account settings and the inbox folder settings to verify that it set to never delete email off the server. I have tried repairing the inbox folders with no change. Other users are also on IMAP and the same domain/host and do not have this same problem. Any ideas that I could be missing?