I’m not getting any new emails. there is an error message and all it says is that "sending email failed due to the following error: The message exceeds the maximum supported size.
Sounds like you have gone over your sending mail server mailbox attachment size and need to either setup cloud drive attachment sending in eM Client V9.x (if this happens alot) and then delete the oversize message in your local folder outbox and send the message again.
Or alternatively just delete the message in your local folder outbox (at the bottom of eM Client) if this has never happened before & was only a onetime thing. See the following eM Client thread for information.