Problema di sinvcronizzazione

I have been your customer for a few years but, lately, I am having problems synchronizing my mail address:
salvatore.spanu1955@gmail.com
which, in fact does not work with mailspring.
I would like to know what and how to do and the correct procedure to include in mailspring also my “old” main address sa.spanu@virgilio.it
which I have, inadvertently, deleted.