The token generator in Mailer.rb (Mailer.token_for) has the following code:

host = Setting.mail_from.to_s.gsub(%r{^.*@}, '')

If you have configured Redmine to send from an address with both name and email, (f.ex. "Redmine Mailerno-reply@redmine.org") this results in a Message-id like the following being created:

>

the double ">" at the end is considered illegal by some mail servers, and results in them rejecting it.

A possible solution could be the following:

host = Setting.mail_from.to_s.gsub(%r{(^.*@)|>}, '')