The TLS 1.2 encryption protocol is required for sending emails via Microsoft 365. AMOffice supports this protocol, but in rare cases it may be disabled. In this case, it can be activated using a specific registry key.
To do this, open the registry editor (Windows key, "regedit" and enter). Under the path HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp\ right-click New → DWORD (32-bit) to insert a new value.
Name this key as DefaultSecureProtocols.
After this has been created, open it with a double-click and enter 'AA0' as the value.
Now sending emails via Microsoft 365 should work in AMOffice.
Note: If the path mentioned before does not exist, HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp\ is a possible alternative