mail doesn't dowload emails

MacBook Pro mid 2012 Catalina 10.15.7. I have a number of Email a/c's - 2 of which are thru' the same Service Provider . The one will download emails while the other will not . The one that doesn't receive emails can however send emails. I have checked all settings & they are correct in fact Connection Docter reports Connected to Server & password correct.

The Provider's server is forwarding emails because I have set up a Gmail a/c and in the settings of the problem Email a/c on the SP's Server I have forwarded all emails of problem a/c to the gmail mailbox in Apple mail.

I also notice that at the bottom of the side window in Mail there is always a message e.g. Downloading 68 of 11,345 . On pressing Get Mail it will change briefly to an actual download of say 5 new messages & then go back to other message ! I noticed this way before the above problem receiving emails started but as it didn't appear to be affecting anything I ignored it.

Any assistance would be appreciated.