With about 60G of accumulated e-mail in several Microsoft accounts, I moved all accounts into T-bird and put most in local folders. This somehow became over 600G in size. Everything works and compacting seems to be getting done since it's been working some weeks now. Yet this ten-fold increase in size is unwieldy and very difficult to backup. Perhaps related, I notice that M'soft's "new" free Outlook app is present and perhaps running on this computer. And all the e-mails I send from my main Hotmail account are listed twice in the T-bird sent folder. About half of the times I start T-bird, I get a message saying that login to server outlook.office365.com with username xxxxxxxx@hotmail.com failed; the other accounts never do this. T-bird offers to retry, but that usually ends with a repeat of the same message. I've learned that if I let it open, with time, the e-mails do appear, though I don't know how or why. I've also been using Libreoffice successfully for months now though I doubt that anything to do with this. T-bird nicely solved the original e-mail oversize problem I had with Microsoft's size limitations and I'd appreciate advice on how to deal with what's happening.