User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.12) Gecko/20080129 Iceweasel/2.0.0.12 (Debian-2.0.0.12-0etch1) Build Identifier: Thunderbird 2.0.0.9 If the real name is encoded and is decoded to "name, firstname", but there are no quotes, thunderbird interprets this as 2 addresses. If doesn't matter whether this concerns "From" or "To". Example: I get an e-mail with the from: From: =?UTF-8?B?RsO8cnN0LCBBcm1pbg==?= <Armin.Fuerst@mydomain.com> And I reply to it, I get to "To:"-Lines: To: Fuerst To: Armin <Armin.Fuerst@mydomain.com> The first line is of course a malformed address. Reproducible: Always Steps to Reproduce: e-mail from: From: =?UTF-8?B?RsO8cnN0LCBBcm1pbg==?= <Armin.Fuerst@mydomain.com> Actual Results: To: Fuerst To: Armin <Armin.Fuerst@mydomain.com> Expected Results: To: =?UTF-8?B?RsO8cnN0LCBBcm1pbg==?= <Armin.Fuerst@mydomain.com>