A bit more info: I have tried clearing Dropbox and done a clean install of Tbird Portable [both 31.3 and 31.1.2] and used just one standard POP3 email account for testing and the same thing happens, the files build up [say a new popstate-xxx.dat about every half hour] and then show in the account pane on lhs when Tbird is stopped and restarted [after Dropbox has got up to date of course]. The same thing happens on Win7 and Win10 machines and laptops. Antivirus is also set to ignore the appropriate Dropbox folders. Help !!!!!!!!!!!!!

As you are using Thunderbird Portable which is from the 'PortableApps.com' website, I would suggest you try their support site. http://portableapps.com/forums/support/thunderbird_portable

The popstate.dat file should be located: Drive letter:\ThunderbirdPortable\Data\profile\Mail\mail account name\popstate.dat

Try this:

• Close/Exit Thunderbid - this is important.

Locate the Profile mail account and delete all the extra 'popstate-xx.dat' files. If you also delete the one which you are supposed to have 'popstate.dat', then it should recreate a new one the next time TB runs.

Thanks Toad-hall but that was the first thing I researched and tried, it then re-downloaded the recent email and unfortunately carried on producing popstate-xxx.dat s etc. I have this afternoon reinstalled with one email account to a SD card and interestingly after a couple of hours and restarts all is still ok. Will next try restoring a recent saved profile, tidy it up and see what happens then. I asked here as I thought this might be the home of the Thunderbird brains trust. Bob.

Thunderbird portable is supported at portableapps.com...

I am not even going there. Thunderbird is not designed to run on anything but a local disk. Portable apps have bent the rules to get it to work on a usb device that is almost as fast as a hard disk, Asking it to work with a profile on dropbox is not going to have a pleasant ending.

Every time you get mail the profile grows... eventually something must give. Sound like it has in your case. But first an foremost get rid of your anti virus scanning stuff... try Windows safe mode. Ohh and a release version of Windows might also help. 6.4 as I understand it is V10 Alpha stuff.

Thank you for the replies.

Installed on an SD card works ok as does an install to a directory on the pc on Windows 7 and 10, the only difference now is that Dropbox is not involved so I can only assume it is the culprit as everything else is the same as it was before. Perhaps I should install to a USB drive and carry it about.

The profile size is as it has been for ages at 80 to 100Mb so I don't think that is a problem, I imagine something has changed with Dropbox file syncing so thank you for the help and I will start looking elsewhere. It is interesting as running Thunderbird Portable from Dropbox has been done by quite a few people for years with no problems.

Best wishes for the new year, Bob.