Office 365 stop supporting TLS 1.0/1.1 at March 1st 2018.
It may required to applying windows patch and registry settings (for application targetting .NET 4.6 or prior version)
Then, it need to ensure old protocols are not used.
Confirm TLS version by Message Analyzer
Use following filter to show only SSL/TLS ClientHello traffics.
(SSL) or (TLS.records.fragment.msg_type == TLS.HandshakeType.client_hello)