Using Let's Encrypt SSL for website and mail

I have an active SSL cert for "domain.com" that is hosted on Server1. If I have a mail service that is hosted on Server2 and uses the same domain root, "@domain.com", would I be able to use the same cert? Or do I need to buy a second SSL for the same domain on the mail server?

>Solution :

1. Your certificate’s SAN (Subject Alternative Name) should either contain both of the target domains or a wildcard domain like *.domain.com.
2. Additionally, the private key must be copied from server 1 to server 2.

If you follow the suggestions above, you should be good to go.