This is on a new installation of Exchange 2010. One or our vendors has a spam filter that they say is blocking outbound mail to our server. with this error" 554 5.7.1 This message has been blocked because the HELO/EHLO domain is invalid. We have not had an issue with any other emails (that we know of). domainA.net MX=mail.domainA.net vendor.com MX=mail.vendor.com when I telnet to my server from one of our clients sites, this is what I get 220 mail.domainA.net Microsoft ESMTP MAIL Service ready at Fri, 19 Feb 2010 09:34:52