Using an SSL cert for Dovecot and Postfix

I currently use a self-signed cert for Dovecot and Postfix but would like to use either a purchased SSL or letsencrypt cert.

I understand that once set up I simply ‘copy to dovecot’ etc, but my question is do I have to keep doing this?

Letsencrypt renews the certificate every few months so would I have to manually copy it over every few months?

Purchased SSL certificates last about 2 years (iirc) so I would I have to make a note to buy then copy over the new cert after that? Or can simply renewing (pay for) the certificate renewal allow the same to be used without having to manually copy things over?

Sorry if this is a silly question…