How you are saving the e-mail on the pen drive is important. To get consistency between computers, the entire Thunderbird Profile should be saved to the "pen drive". Thus not only are the e-mails on the pen drive, but all your Thunderbird settings are on it also. This would include the tag definitions. See [https://mzl.la/2lBfidM Profiles - Where Thunderbird stores your messages and other user data]. So I recommend that you [http://brucejohnson.ca/ThunderbirdProfile.html create a new Thunderbird Profile with the location on the pen drive, then import all your stuff from the old Profile to the new one]. <blockquote>Also, my company send the Incoming mail after one month to another folder automatly and in this change the tags are deleted</blockquote> I believe that the tags are only in Thunderbird, so the e-mail on the server remains the same. If you move an e-mail from one folder to another in Thunderbird, then Thunderbird will retain the tags. If something other than Thunderbird moves the e-mail, it appears that Thunderbird is not smart enough to recognize the move, and transfer the tags for the e-mail.

You can try this: http://www.grimeton.com/custom-tags-with-thunderbird-stored-on-imap-server/ I don't if it will work for you or not.

Thanks Bruce. It doesn't work but thanks anyway.