Using Windows-10 and up-to-date T-Bird. I have three pop3 accounts. When I try to receive any message (any account) I get pop-up saying: "there was an error in downloading the following message <message description> this message may contain a virus or there is not enough disk space." When I try to send I get a pop-up saying: "Your message was sent but a copy was not placed in your Sent folder due to network or access errors" When I try to delete any message the pop-up says: "message could not be moved or copied to folder 'trash' because writing to folder failed. To gain disk space... first empty trash... then compact folders" This happens in all three email accounts. I can't peg it to any updates from either T-Bird or Windows. Have made no setting changes to T-Bird. Email accounts work fine using T-bird on different computer. I think I have eliminated possibility of anti-virus interference by both turning off and setting exclusions for mail folder. edit: forgot to mention that folders were not over-full and compacting is done regularly. I'm stumped! Any suggestions appreciated. (I can't see any way to add the Troubleshooter "Application Basics" text. The "Add" posting button only sees image files, and the text is too long to copy/paste here. Sorry if i'm missing something.) Many thanks.