554 sorry, your envelope sender is in my badmailfrom list (#5.7.1)

Q.When I try to send email via SMTP, I am getting the following error 554 sorry, your envelope sender is in my badmailfrom list (#5.7.1). What am I doing wrong?

A. We have a default 100 smtp emails/day on all customer accounts at the UDC to prevent spamming. Spamming can cause us to become listed on a email blacklist which will mean ISPs will block our mail server ips. This will affect ALL our customers email services so this strict policy is in place.

Please note: Our new Dallas network will not have such a strict policy and you can request to be moved to the new network (eventually everyone will be migrated).

That said, we will still be strict on fighting spam and being blacklisted and will take action should this occur.