If there is a mailing list and a contact with the very same name in your address book, a message composed to the contact is actually sent to the mailing list. 1) Create a new contact with the name "Test" 2) Create a new mailing list with the name "Test" 3) Write a new message and add the contact "Test" in the To field 4) Send the message using either "Send Later" or "Send Now" Result: The message is sent to the mailing list instead of the contact! If you use "Save as Draft" or "Save as Template", the saved message correctly contains the contact in the To field. The problem occurs only for "Send Later" or "Send Now". There are a few reports about this problem in the German Thunderbird forum: http://www.thunderbird-mail.de/forum/viewtopic.php?f=39&t=67194 http://www.thunderbird-mail.de/forum/viewtopic.php?f=31&t=67223 The problem might be related to: https://bugzilla.mozilla.org/show_bug.cgi?id=1044559
Both the contact and the mailing list must be in the very same address book. If they are in different address books, everything works fine.
I tried the suggested nightly builds as mentioned here: https://bugzilla.mozilla.org/show_bug.cgi?id=1008718#c6 2014-03-03: works! ftp://ftp.mozilla.org/pub/thunderbird/nightly/2014/03/2014-03-03-03-02-04-comm-central/ 2014-03-05: doesn't work! ftp://ftp.mozilla.org/pub/thunderbird/nightly/2014/03/2014-03-05-03-02-02-comm-central/ It looks like the problem was introduced in 2014-03-05.
Thank you for testing and steps to reproduce. Let's mark it a dupe for now.