In this post, I would like to highlight that Microsoft has scheduled a “24-hour test that switches Microsoft Teams Direct Routing SIP endpoints to certificates issued by a new Certificate Authority (CA)” as communicated via the Microsoft 365 Message Center MC1387525.
Starting June 30, 2026 (9:00 AM UTC), Microsoft will run a test lasting up to 72 hours due to staged regional rollout to transition Direct Routing SIP endpoints to new CA-issued certificates. This aims to improve certificate lifecycle management and maintain secure connectivity. During the test window, organizations using Session Border Controllers (SBCs) for Teams Direct Routing may experience a mix of old and new certificates, as traffic is gradually migrated. If SBCs do not trust the required Root CAs, TLS connection failures may occur, which could lead to disruptions in PSTN calling. So ensure you certificates, certificate chains etc. are alright on your Teams Direct Routing SBCs.
The change will be applied automatically by Microsoft and reverted after the test period. Organizations are required to proactively verify and if necessary update SBC trust stores, inform relevant voice and support teams, and closely monitor connectivity and TLS handshake behavior throughout the test to mitigate potential service impact.
erik365.blog 
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