On Monday we released version 14.4 of SmarterMail which includes a fix for syncing Outlook 2016 using IMAP where many SmarterMail folders had a UID validity value (UIDVV) of 0. According to the IMAP RFC these UIDVV values can not be 0.
We fixed this by changing any UIDVV values of 0 to 1 when an account's folders are loaded.
The purpose of the UIDVV value is to tell an IMAP client if a folder with a particular name has been deleted and then recreated with the same name. So if I delete my Sent Items folder and then create a new folder named Sent Items, the UIDVV value will increase and IMAP clients will know they must re-sync that folder from scratch.
Due to the nature of this issue there is no way to fix it without forcing IMAP clients to re-sync all folders that had a UIDVV value of 0.
This will cause a large spike in resource usage after installing this new version until all the IMAP clients have re-synced the affected folders.
We have received a number of tickets related to this since the Monday release so we will revert the current release back to 14.3 for now and will release a new version later today that will only apply the fix to a set number of accounts per hour to limit the impact on resource usage.