Rescue SMTP errors when sending suspension mailers

also, ensuring we retry only on errors where
it makes sense to retry: like timeouts and
server busy errors.

related reading:

http://robots.thoughtbot.com/i-accidentally-the-whole-smtp-exception
http://ruby-doc.org/stdlib-2.0/libdoc/net/smtp/rdoc/Net/SMTP.html#method-c-start-label-Errors
It would be good to still send the exception to errbit (with the context), and also, this shouldn't prevent the following users from being attempted.  It probably makes sense to convert this to a blanket rescue instead of the specific one that it is now.  What do you think?