User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.12) Gecko/20050915 Firefox/1.0.7 Build Identifier: Mozilla Thunderbird version 1.0.7 (20050923) When I receive an e-mail with multiple recipients and some of them have national characters and a comma inside written like that: To: =?iso-8859-2?Q?P=B3aszczka=2C_Anna?= <abcd@efgh.ijkl.opq>, <xyz@aa.bb> Thunderbird interprets a comma in the iso-encoded address and handles this address as two: Plaszczka (WITHOUT real e-mail address) Anna <abcd@efgh.ijkl.opq> When choosing Reply-All this results in send errors since some recipients do not have a valid e-mail address. This kind of addresses seems to be produced repeatedly by: X-MimeOLE: Produced By Microsoft Exchange V6.5.7226.0 where the administrator decided to use real user names like that: Surname, Firstname Reproducible: Always Steps to Reproduce: 1. You need to receive a "properly" formatted e-mail with one of the recipients encoded like that: To: =?iso-8859-2?Q?P=B3aszczka=2C_Anna?= <abcd@efgh.ijkl.opq> 2. Observe recipients list when viewing the email 3. Try to reply-all Actual Results: Two recipients appear instead of one: Plaszczka Anna <abcd@efgh.ijkl.opq> Expected Results: Only one recipient with quoted "Plaszczka, Anna" <abcd@efgh.ijkl.opq> should appear.

Duplicate of Core bug 254519?

Yes, a dupe. *** This bug has been marked as a duplicate of 254519 ***