SQL Server Database Mail cannot send email smtp.office365.com

Question

SQL Server Database Mail cannot send email smtp.office365.com

Hi, I try to use SQL Server Database Mail, and I get this error:

The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 7 (2025-04-02T16:57:33). Exception Message: Cannot send mails to mail server. (Error in processing. The server response was: 5.7.3 STARTTLS is required to send mail [LO4P265CA0007.GBRP265.PROD.OUTLOOK.COM 2025-04-02T11:27:32.964Z 08DD7161F6BFCBDA]).).

The configuration I use is:

Server: smtp.office365.com

Port Number: 587

Authentication: Basic (An email address and password)

I am able to telnet from the server to smtp.office365.com on port 587.

I can send email within my organization but getting this error only while sending email to outside world.

Answer 1

Office 365 requires tsl and no longer supports basic authentication. You will need a smtp proxy/relay to use basic authentication

https://techcommunity.microsoft.com/blog/exchange/exchange-online-to-retire-basic-auth-for-client-submission-smtp-auth/4114750.

note: sql mail uses smtpclient which is not being updated to support oauth authentication.

Answer 2

To talk to MS365 your SQL Server must be using SSL and it must be using TLS 1.2. You didn't mention what version of SQL you're running. Ensure that SQL is configured to use TLS 1.2 as discussed here.

Also ensure that you have checked the option in the configuration to use SSL.