SMTP XOAUTH2 Authentication Problem for GoDaddy accounts

Question

Dear Sir/Madam,

We are following Microsoft authentication instructions to connect with IMAP, POP or SMTP here https://learn.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth
After OAuth authentication we receive tokens for the following scopes:

https://outlook.office.com/IMAP.AccessAsUser.All
https://outlook.office.com/SMTP.Send

IMAP connection works fine, but we have issues with SMTP.
We connect to smtp.office365.com server, port 587, using STARTTLS protocol.
When attempting to authenticate using standard format AUTH XOAUTH2 <base64 string in XOAUTH2 format> we get error: “NO AUTHENTICATE failed.”.
When attempting to authenticate by 2 consecutive requests, we get the following error:
C: auth xoauth2
S: 334
C: <base64 string in XOAUTH2 format>
S: 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant.

It is important to note, that this problem only occurs for accounts with domains other than outlook.com. For example, for accounts migrated from GoDaddy (<user_name>@intechcenter.com, where "<user_name>" is a mailbox name on “intechcenter.com" domain).

Please help us to understand how we can resolve these errors.
Thank you!

Answer 1

Hi @Vladimir Luchkin ,

535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant.

Please have a check that mailboxes migrated from externally have authenticated SMTP enabled.
If not, you could refer to the following steps to enable SMTP AUTH on specific mailboxes. Then try again to see if the authentication was successful.

1. Open the Microsoft 365 admin center and go to Users > Active users.
2. Select the user, and in the flyout that appears, click Mail.
3. In the Email apps section, click Manage email apps.
4. Verify the Authenticated SMTP setting:
5. Check Authenticated SMTP to enable it.
6. When you're finished, click Save changes.

---

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.