[CentOS] Forcing TLS for SMTP?

Phil Perry
Wed, 04 Dec 2019 22:24:51 -0000

On 04/12/2019 22:03, Lists wrote:
> I have a goal of securing email. Updated the company mail server and DNS
> (CentOS 7 + Postfix, otherwise pretty stock) with support for SPF, DKIM,
and
> DMARC. So far, all good, and everything "just works".
>
> Our mail server has supported SMTP / TLS for a long time, but recently
I've
> been considering requring TLS all the time.
>
> Is there anybody here who's done this? Has it caused any particular
fallout?
> I'm curious about:
>
> 1) Requiring SMTP / TLS for any inbound email.
>
> 2) Requiring SMTP / TLS for any outbound email.
>
> Thanks
>

The obvious consideration is that if the other server does not offer
tls, the connection will fail and you will not be able to communicate.

Further RFC2487 states that enforcing tls must not be used on public
facing mail servers.

So if you want to enforce tls to ensure encryption on purely internal
mail servers, that is fine but your external facing smtp servers must
not enforce tls.

See the Postfix tls documentation for more information: