We are receiving an error message when we try to send mail to one specific domain. Our spam filter has this domain whitelisted, soI don't see it being quarantined in there. Delivery status : Failed. Message could not be delivered to domain <xyz.com> .Failed while initiating the protocol. <[('person@xyz.com', 553, 'sorry, your envelope sender is in my badmailfrom list (#5.7.1)')]> MTA Response :553 I am not even sure where to begin to troubleshoot. The company we are trying to send email to says that it is not on their end.

That 5.7.1 is a generally a spam block. Check all three lists below for your IP. http://www.spamhaus.org/ Also, maybe find out what other block list providers the recipient is using and find out why you are on the list.

My institution has been the target of many phishing scams. I'm sure that's why our domain is on any spam lists. Thank you for your help.

To help protect against phishing scams, I'd highly reccomend implementing SPF if you haven't already (MS Calls it SenderID Framework..same thing) Www.openspf.org has a wizard for setting up the dns records and explains SPF.