Exchange Online will retire legacy TLS versions (1.0 and 1.1) for POP3 and IMAP4 connections from August 1 to December 31, 2026. Connections must use TLS 1.2 or later; older versions will fail. Organizations should ensure all email clients and applications support TLS 1.2+ and update legacy systems accordingly.
Applies to: Exchange Online
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).