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davidc0015
Known Participant
August 5, 2026
Question

Cloud Customer: SMTP Setup with M365 Not Able to Send Outbound Emails

  • August 5, 2026
  • 7 replies
  • 53 views

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

7 replies

shubhama926776
shubhama926776
Brainy
August 6, 2026

Both errors come from M365, so M365 is receiving the mail and rejecting it as an unauthenticated relay. Not Appian, not your firewall.

Recommend, Create an Exchange Online connector that authorizes your environment's outbound IPs with valid TLS. That is what allows external relay. Get the current IP list from Appian Support.

https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/how-to-set-up-a-multifunction-device-or-application-to-send-email-using-microsoft-365-or-office-365

शुभम्
D
davidc0015Author
Known Participant
August 6, 2026

Hi Shubham, Appian Support provided a worksheet to us and we chose TLS enabled as false. Any other recommendations you have have?

shubhama926776
shubhama926776
Brainy
August 6, 2026

Out of curiosity, was there a specific reason TLS was set to false? That handshake failure in Error 1 makes me think enabling TLS is worth testing.

शुभम्
harshas2775
harshas2775
Brainy
August 6, 2026

Follow this microsoft article to resolve the error you are getting. If the error persists Microsoft Support team will be able to help you in resolving this, not Appian or your company’s network team. 

mathieud0001
mathieud0001
Brainy
August 6, 2026

Client SMTP submission using Basic authentication in Exchange Online is scheduled for deprecation, see timeline information. We strongly recommend using one of the following alternative methods instead:

  • Send email to internal recipients only: Use High Volume Email for Microsoft 365. For instructions, see Manage High Volume Email for Microsoft 365.
  • Send email to internal and external recipients: Use Azure Communication Services Email. For more information, see Email SMTP support in Azure Communication Services.
  • If you have one or more on-premises email servers (Exchange Server or any other SMTP server), you can use one of the following methods:
    • Use Basic authentication to authenticate with the on-premises email server.
    • Configure the on-premises email server for anonymous relay (not open relay). For instructions in Exchange, see Allow anonymous relay on Exchange servers.

Client SMTP submission using Basic authentication isn't compatible with Security defaults in Microsoft Entra ID. We recommend using Modern authentication (OAuth) to connect to our service. For more information about OAuth, see Authenticate an IMAP, POP, or SMTP connection using OAuth.

Basic SMTP auth is deprecated. I would also log a ticket with Appian to add more types of authentication for SMTP (i.e. OAuth).

mathieud0001
mathieud0001
Brainy
August 6, 2026

Basic SMTP auth is deprecated. I would also log a ticket with Appian to add more types of authentication for SMTP (i.e. OAuth).

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