One user's bad email address breaks all email notifications for everyone on a project
Because everyone's email address is used in one email, if a mail server rejects the message because one address is bad
and it hosts that domain, then no notifications are ever sent for any project that the bad user is a part of.
Example: Say I have A.A, B.B, and C.C @foo.com. If B.B lists his email as B-B@foo.com then the mail server at foo.com
(which is the one redmine is using) will reject the address, and thus the message.
Redmine should send one email per addressee rather than one group email OR have the option of sending all notifications
for the project to one address so someone can setup a mailing list and then one email to the person that owns the object
that generated the notification (an issue's assigned owner, for instance).