[MlMt] Remove a bogus address from "To" address completion?

[Kai Großjohann]

I exchange a lot of email with John Doe, but somehow, 
"jdoe at example.comkai" ended up in the list of "To" addresses to be 
completed.  The correct address (the one without "kai" at the end) is 
also in the list, but the wrong one seems to come first.

How do I remove the bogus "jdoe at example.comkai", leaving only the valid 
"jdoe at example.com"?

The bogus address is not shown in the "Contacts" application, that one 
only contains John's valid address.

Kai