The issue of Outlook mobile apps being unable to refresh emails after an update could be related to several factors. One potential cause is the compatibility of the app with the Exchange Server version. Since you mentioned that the backend server is Exchange Server 2019 with the latest Cumulative Update (CU) and Security Update (SU/HU), it is important to ensure that the server is configured to support the latest TLS protocols. Outlook for iOS and Android requires TLS 1.2 or later for secure connections, and if the server is still using deprecated versions like TLS 1.0 or 1.1, this could lead to connectivity issues.
Additionally, if the TLS certificate on the server is expired or not installed correctly, it can also prevent the Outlook app from refreshing emails. It would be advisable to check the TLS settings and the validity of the TLS certificate on your Exchange Server.
If the problem persists, consider checking for any known issues with the specific version of the Outlook app that was updated, as there may be bugs or compatibility issues that need to be addressed by Microsoft.
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