Hi, I have the same problem since the last bigger update of Thunderbird. Seems like the logic has changed and now every time something is done with any mail, the Windows Defender interrupts and uses 1-2 CPU Cores to scan for about 1 minute per mail or action. I can reproduce this issue with any e-mail action. - click on it - mark is as junk - delete it - receive it Thunderbird is now (after so many years) unusable for me. And with all the recent spam mails on my accounts Thunderbird now needs more than an hour to receive all mails. This wasn't a problem before the 102.x version of Thunderbird. I would guess that something in the code makes many small reads what was formally just read once (or out of memory) and now the Windows Defender scans the the accessed files every time. And no, it is not an option to exclude Thunderbird from the Windows Defender. With all those spam mails in recent times, there are also often viruses/trojans in the attachments, I still want the system to get rid of those. I do not use any extensions oder addins in Thunderbird. Just Plain Thunderbird (for years now). OS is lastest Windows 11.