It turns out this is more of a story of finding a fix as I seem to have resolved it... This morning I updated to TB v102.3.0 (64-bit). Not sure of the version I had before, but it was less than a few months old. Every 2 or 3 months, I move mail out of my inbox with the expectation it will keep the server and email client from significant delays while loading messages. There were about 500 messages when I started this morning which took about 20MB on disk according to the folder properties window. The folder I'm moving messages to has 1500 messages and takes 70MB on disk. I'm finding that when I move many... say 30 - 50 messages from Inbox to the other folder, there is a delay over a minute. I'm thinking this much delay doesn't make sense considering I was not experiencing this kind of delay before updating TB and my primary hard drive with OS and TB an SSD. During this delay, Windows Task manager shows 0 - 1% CPU usage on the thunderbird.exe processes. Nearly a flat line for the SSD for both active time and disk transfer rate. A jump to 10% for active time during the first 2 seconds, then 0-2% for at least 10 seconds. Moving 5 - 10 messages is also taking close to 10 seconds where it would have been instant before. Updated to v102.3.1 while writing this. Same symptoms after. .... What seems to have removed the delay is using Repair Folder on the destination folder. Now that nearly instant (1-2 second) response is back. Is this a new bug with the v102.3 update? If so, could it be automatically resolved by checking something about the existing local data needs repair or updating? Thanks to the developers and community that support TB development.