I have just noticed that my emails have stopped being generated by actionmailer Net::SMTPFatalError (553 Invalid mail address)
This is a known problem and is really hard to track down. See https://rails.lighthouseapp.com/projects/8994/tickets/2340-action-mailer-cant-deliver-mail-via-smtp-on-ruby-191
Some others are getting slightly different messages but it all revolves around the name format
It affects 2.3.3 and 2.3.4 and also an issue on ruby 1.8.7 and 1.9.1. It is scheduled to be fixed in 2.3.5
There is a workaround.
I hope posting this here will help someone else google this error. I couldn't find anything on the group archive.
O.