I am a faithful user of the DominoTeamMailbox (created by Brian Green) available at OpenNTF.org. In recent attempts to send mail from the database, the delivery is stopped (usually by large email providers like yahoo and gmail).
Here is an example of the error I receive when trying to send to gmail addresses: Error transferring to gmail-smtp-in.l.google.COM; SMTP Protocol Returned a Permanent Error 550 5.7.1 more information. e188si2055049qhc.102 – gsmtp
Here is an example of the error I receive when trying to send to yahoo addresses: Error transferring to mta7.am0.yahoodns.net; SMTP Protocol Returned a Permanent Error 554 Message not allowed – Headers are not RFC compliant
SOLUTION: Use the email address as the mailbox title.