Connections to Microsoft 365 require at least TLS 1.2 (see M365 supported cipher suites). Some of the services (including Teams) make use of Azure Front Door to terminate TLS connections. Because of that the list of supported Azure Front Door TLS cipher suites defines the cipher suites which must be enabled for Veeam Backup for Office 365. Enable at least one of the following cipher suites on your VB365 and proxy servers. The suites are already listed in preference for security with the top secure one being on top. The
ECDHE key-exchange type suites are available from Windows Server 2016 onwards.
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
Customers have also reported success using third party applications such as IISCrypto for updating cipher suites and TLS versions on systems running Windows Server 2012 R2 and older.