You can select tag T in the source list, select the relevant records, and then press Delete to remove tag T.
To find the relevant records, normally you could just search with the tag selected, however, although the search field supports negation you must enter at least one search term that is not negated. So the obvious technique doesn’t work in this particular case.
Here are some ways that I can see to do what you want:
- Make a smart folder like:
All of the following:
[INDENT]Tags contains T
Anywhere does not match “firstname.lastname@example.org”
Set the action of the smart folder to remove tag T. Then drag the contents of the smart folder onto the smart folder (to apply the action).
- This way is more complicated but may illustrate a technique that you find useful elsewhere:
- Make sure Match Partial Words is not checked.
- Create two new tags, RemoveT and Wrong.
- Select tag T in the source list and select all the records; drag them onto tag RemoveT so that they all have both tags.
- With tag T still selected, do an Anywhere search for “email@example.com”; select and drag all the matches onto tag Wrong.
- Select tag RemoveT and do a Tags search for Wrong; select all the matches and press Delete.
- Select tag T and do a Tags search for RemoveT; select all the matches and press Delete.
- Delete the temporary RemoveT and Wrong tags.