Yes, they are rejecting a select amount of traffic on older protocols, and will gradually reject more, annoying people into upgrading their equipment/protocols.
New opt-in endpoint available for SMTP AUTH clients still needing legacy TLS - Microsoft Tech Community
From the link:
With this in mind, starting in September 2021, we will reject a small percentage of connections that use TLS1.0 for SMTP AUTH. Clients should retry as with any other temporary errors that can occur during submission. Over time we will increase the percentage of rejected connections, causing delays in sending that more and more customers should notice.
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