I have the fax server set up, it's taking in the faxes fine, generating nice PDF's, and sending them out. Should be all great right? We have an HP fax machine with Web services, one of them being it's own personal email: ***@hpeprint.com We just switched to 3CX from a different system that was handling incoming faxes and emailing to the fax machine with no problems. However, the 3CX's emails are being rejected by the hpeprint mail servers. I'm getting this error on bounce back: The response from the remote server was: 550 5.7.1 Command rejected Final-Recipient: rfc822; ****@hpeprint.com Action: failed Status: 5.7.1 Remote-MTA: dns; onramp01.hpeprint.com. (126.96.36.199, the server for the domain hpeprint.com.) Diagnostic-Code: smtp; 550 5.7.1 Command rejected Last-Attempt-Date: Thu, 22 Jun 2017 09:04:22 -0700 (PDT) any ideas on what might be causing the problem? thanks for the help!