Cloud Customer: SMTP Setup with M365 Not Able to Send Outbound Emails
Hi Appian Community, wanted to see if anyone has this setup of being an Appian Cloud customer and has email server setup with Microsoft 365 cloud SMTP relay, specifically for outbound emails from Appian → External Recipients?
I am able to receive outbound emails from the Appian platform with my organization’s internal email addresses. The problem is when testing by sending to external email addresses (both business email addresses, tested by sending to @microsoft.com and personal email addresses, tested by sending to @gmail.com and @hotmail.com). They failed with 2 different error messages from the STDout log:
Error 1 (Attempt to send to external business emails):
451 4.4.62 Mail sent to the wrong Office 365 region. ATTR35. For more information please go to https://go.microsoft.com/fwlink/?linkid=865268 [Full certificate chain to a Microsoft-trusted Root CA was not found in TLS handshake. See https://aka.ms/UntrustedRootNdr for more] [YT2PEPF000001C9.CANPRD01.PROD.OUTLOOK.COM 2026-08-04T20:16:46.794Z 08DEEF55C1ED64AF]
Error 2 (Attempt to send to external personal emails):
451 4.4.4 Mail received as unauthenticated, incoming to a recipient domain configured in a hosted tenant which has no mail-enabled subscriptions. ATTR5 [YT2PEPF000001CF.CANPRD01.PROD.OUTLOOK.COM 2026-08-04T16:00:03.543Z 08DEEF639E6DF98A]
Some more background, our organization’s cloud setup with Appian is connecting via a VPN tunnel and we have whitelisted in our firewall rules to allow traffic to and from Appian to our company’s on-prem connections.
We have included all of Appian’s site names in the organization’s SPF records and enabled DKIM.
Questions:
- Did anyone also need to update their organization’s firewall rules to whitelist the new cloud M365 relay?
- Anyone came across those 2 error messages? Any troubleshooting steps would be appreiated