@DocEames My issue occurred before up grading to Big Sur, so it existed previously with Catalina. I honestly think I recall having this issue years ago, different employer and like 7 years ago but on the whole, I've not had issues where Mail never seemed like a poor alternative to the Outlook app. In my entirety, it's been probably 4 days total that I experienced the issue. Have you tried clearing the trash/junk maybe even old folders of saved mails and attachments? I found that the app CleanMyMac X has a feature to go through and remove the local copies of attachments to email, which in my business can be large files. The file still lives on the server so if I open an old saved email with an attachment that the local copy has been removed it automatically re-downloads the attachment.
Not sure if i mentioned on this thread before, but my wife's company iMac she works on from home now, if she runs the Outlook app, after some point, or load on the computer, the screen will blink out, on off, white and black flashes and feels like a graphics card going bad. BUT shut down the Outlook app and problem goes away. She now uses Outlook in a web browser and I keep telling her I'll help her set up the Map app to do the Exchange account. HA
