Marco Marco writes writes:

I've bought a certificate from the authority for my website to use to access in https mode.

Is it possible to share the same pairs to authenticate the emails sent by postfix and Dovecot in order to avoid that client as Hotmail.it or Gmail intercept these as Spam?

By "same pairs", I assume you mean key and certificate.

Yes, just as long as you use the same Subject for all your services (e.g. "mail.yourdomain.com") or you have purchased a wildcard certificate e.g. "*.yourdomain.com" to authenticate "webmail.yourdomain.com", "imap.yourdomain.com", "smtp.yourdomain.com", etc.)

Certificates do not authenticate services or protocols, but server names (typically).

Joseph Tam <jtam.home@gmail.com>