1

Certificate from GoDaddy is in place, I have removed esmtp inspection from our Cisco ASA, and hybrid mail is flowing from Office 365 to our on prem Exchange 2013 server. When trying to send mail to a mailbox migrated to Office365 I am receiving the dreaded '451 5.7.3 STARTTLS is required to send mail".

Since our MX is pointing to a 3rd party mail filter I changed the on prem connector created by the hybrid config wizard to relay mail through 'ourdomain-com.mail.protection.outlook.com'

I am also able to telnet directly from our Exchange server to ourdomain-com.mail.protection.outlook.com 25. An ehlo shows the STARTTLS verb IS available.

Kind of hitting a wall here. I would greatly appreciate any insights from the community!

1
  • I forgot to add that we are also not blacklisted (checked via mxtoolbox). Thanks! – Christopher Dallas Jun 8 '16 at 19:59
1

In our network we have a router out in front of our ASA.

I had overlooked CBAC smtp inspection. I removed this statement on the router, re-ran the HCW, modified the On Prem connector to 365 to point to domain-com.mail.protection.outlook.com, and now Hybrid is working as intended.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.