Just during the last month or three Thunderbird has become extremely slow in deleting messages. It's not my antivirus. I'm using Windows Defender, always have and nothing has changed there. I'm using Windows 8.1. Thunderbird worked fine until recently, then all of a sudden it's started taking 10 seconds or so to delete each message. Multiply that by 20 or 30 messages a day, and that's a real time waster. There seems to be a logic bottleneck somewhere. Files should work quickly regardless of size. Whether random or sequential filing, 100 records or 100,000 records, should be just as fast. Tells me the logic is messed up somewhere. I am a professional programmer with some 35 years experience. None of my other programs have slowed down. No other part of Thunderbird has slowed down-- only deleting messages. I've tried cleaning trash, compressing files, etc. Educated opinion: logic bug.