[GTALUG] SSL Certs for both web and email servers

Hi! Can I use the same SSL (from letsencrypt) cert for both web and email traffic? I have three domains and a small but invariant number of subdomains that I want to encrypt - should I try to pull them all under one SSL cert, or do one for each domain, or one for every subdomain? I don't need a wildcard, but I would like something relatively painless if possible. I use Apache2 for web (running virtual servers) and Dovecot for inbound email. There are a lot of old tutorials, but I haven't found one that answers my questions quite yet. Thanks!