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.īefore diving into further details, keep in mind that generally speaking, the TLS implementation in Exchange on-premises or Exchange Online is done opportunistically. We wanted to talk about what this means for SMTP traffic destined to Exchange Online in particular. Also note that Exchange Online will never use TLS 1.0 or 1.1 to send outbound email.
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. The rollout will continue over the following weeks and months. 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. 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. 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.
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