Mail_Queue Plugin working in Development, but not Production

I’ve got the Mail-Queue plugin working for development, and it was
recently (2 weeks ago) working in Production mode, too. But now it’s
not.

This is what happens if I run “ruby script/runner MailQueue.process -e
production” on the production server:

/usr/lib/ruby/gems/1.8/gems/rails-1.2.3/lib/commands/runner.rb:47:
/usr/lib/ruby/1.8/net/smtp.rb:680:in check_response': 501 <>: missing or malformed local part (Net::SMTPSyntaxError) from /usr/lib/ruby/1.8/net/smtp.rb:653:ingetok’
from /usr/lib/ruby/1.8/net/smtp.rb:635:in rcptto' from /usr/lib/ruby/1.8/net/smtp.rb:546:insend0’
from /usr/lib/ruby/1.8/net/smtp.rb:545:in send0' from /usr/lib/ruby/1.8/net/smtp.rb:472:insendmail’
from
/usr/lib/ruby/gems/1.8/gems/actionmailer-1.3.3/lib/action_mailer/base.rb:567:in
perform_delivery_smtp' from /usr/lib/ruby/1.8/net/smtp.rb:379:instart’

Has anyone advice on this matter?

Concerned,
Joe

I’ve got the same ActionMailer::Base.smtp_settings in both production
and development environments, yet mail-queue only works in development.
Anybody know why?

Mail-queue is catching all the emails and storing them, but seems unable
to send them.