Cannot get mail - Apple Watch Ultra 2

Issue Description: When i leave my iPhone at home and I'm away using only my Apple Watch's cellular connection, I cannot receive emails. The Watch displays the following error message:

Current Behavior:

• Emails work fine when iPhone and Apple Watch are together
• Cellular connection appears to be working (signal bars visible)
• Error only occurs when Watch is on cellular without iPhone nearby

This happens with Exchange and Gmail accounts. Can someone help?