Understanding email scenarios if TLS versions cannot be agreed on with Exchange Online

By now you are hopefully aware of the TLS 1.0/1.1 deprecation efforts that are underway across the industry and Microsoft 365 in particular. Head out to our documentation for more details and references if you need a refresher! Also check out this blog entry to see how you can use reporting in Exchange Online to get an overview about the TLS versions used by mails submitted to your tenant. This topic may be super-relevant to you, because as confirmed by the message center post MC229914, TLS 1.0 and TLS 1.1 deprecation started enforcing for Exchange Online mail flow endpoints beginning January 11th, 2021. The rollout will continue over the following weeks and months. This essentially means, soon this deprecation process will be over, and we will no longer accept TLS 1.0 and TLS 1.1 email connections from external sources. Also note that Exchange Online will never use TLS 1.0 or 1.1 to send outbound email.

We wanted to talk about what this means for SMTP traffic destined to Exchange Online in particular. What happens if a server on your side can only use TLS 1.0 with SMTP? Will sending fail, and if yes, how do you notice TLS 1.0 or TLS 1.1 is the root cause of your email problems? There are different variables that impact this and we will try to mention most frequent scenarios.



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Printed on: November 30, 2021 at 22:11 o'clock

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