ta Milo, it is not the "show attachments inline" that is causing the problems, the attachments (like a 5Mb .mpg file) are being shown in ASCII, not good for non text documents, the header info (all internet nodes the mail passes through en route are being displayed) is all being shown in line, the subject in the email is not showing in the inbox list and the sender is not showing in the inbox list.
I cannot find anything in the Thunderbird setup which controls how incoming file data is interpretted, all of the options for file format control the sent mail encoding.
Today I have un-installed Mail Washer and removed some remnants of Eudora mail browser from the system. The problems persist.
I then configured another machine to read (but leave on server) the same host mailbox, this has confirmed that the emails on the server are not messed up. So it is something in my partners system that upsets the format of incoming email.
She has Win XP, fully updated, AVG, Zone alarm and the latest Thunderbird. We are sure that it is not a Thunderbird issue as the email format is broken when it is scanned by Mailwasher.
This leads us to look for something else in her system. What else might corrupt incoming email between the ethernet port and the inbox? When she was using Eudora as a mail browser she had endless issues with many messages being received multiple times, everything with an attachment came in up to 8 copies!
Something is strange in her machine when running mailtools. Otherwise the machine is fine, stable, capable etc.has yet to show the blue screen of death or need rebooting without good reason. The hardware is two years old.