My backup email error handler noted a few errors in the windows event viewer, the specific error was
The EXECUTE permission was denied on the object ‘sp_send_dbmail’, database ‘msdb’, schema ‘dbo’.
If you have receieved this, then you need to add the user to the database by going to properties of the user and editing the “mapping” ensuring that said user is ticked next to the db “msdb”
Then run the follwing trasact against he msdb daabase replacing the word user here with the user you need to apply this to.
Grant EXEC on sp_send_dbmail to user