Disable email scanning in your anti virus product and try again.

Matt, checked the email virus scanner (Symantic Corporate) and it was not turned on. I seem to recall being advised that Tbird was just a client that got the messages from Yahoo so it was already checked before Tbird got it, that was about 10 years ago though. I enabled it but made no difference. Updated to a newer version of Tbird and changed password, no good. Run a full virus scan, ran malware antibytes, PC rescue and Glary. Each time I turn it on now an old message (from spam folder) from 7/7/14 appears after the message downloading 52 messages blah blah. It was previously downloading another message from the spam folder but I had created a filter to auto delete that one. Incidently the same date/time is displayed each download. there is still a nasty lurking but how do I find the bugger?

That description sound a lot like folder corruption. (same date) Compacting a folder clears corruption, but it is very aggressive with mail and data loss usually occurs if the folder is corrupt.

So move mail from the folder to another then right click the folder and select compact.

If that does not work, log into Yahoo using a browser and empty your spam foplder and see if that helps at all.

Thanks Matt, had tried compacting folders several times but no good. However when I emptied the spam folder and restarted Tbird all was well with the world. i was looking for something sinister and complicated when all I had to do was delete the message that was duplicating itself. Thanks again, great job. Bruce