With PKIX validation the certificate should match the hostname.
With SMTP, the hostname should match the reverse IP though often it does not.
Using subdomains gives you flexibility.
with DANE validation, it is DNSSEC that validates the fingerprint to the hostname so I do not believe there is a need for the hostname in the cert to match anything, but DANE validation is currently not used by any mail user agents, only PKIX validation is used by mail user agents.
DANE is used to MTA to MX quite frequently however, so it may come to mail user agents in the near future (near being within a decade or so).
On 3/14/19 10:03 PM, Gary via dovecot wrote:
Is there some reason to use a mail.domain.com cert for mail rarher than just using domain.com for everything?
Historically the subdomain were used because they were on different hardware. That is www was on one machine and mail was on another.
Original Message
From: dovecot@dovecot.org Sent: March 14, 2019 3:56 PM To: dovecot@dovecot.org Reply-to: jtam.home@gmail.com Subject: Re: regarding ssl certificates
mick crane wrote:
Apache2 default install has this snake oil certificate Can make a new one for apache
I won't go over some of the excellent points in previous posts, but I will mention SAN as a third type of certificate you can make. LetsEncrypt supports this type of certificate.
This is halfway between single CN and wildcard certificate where you can combine many hostnames (up to 1000?) into one certificate. This may be useful if you want the convenience of handling fewer certificates, without having an unbounded wildcard certificate (the latter also requires control over your DNS). I use this for SMTPAUTH, POP3, IMAP and webmail services since they are all on one server.
Then Stephan von Krawczynski wrote:
Sorry I have to write this, but this is again pointing people in a fake security direction. The only valid authority for a certificate is the party using it. Any third party with unknown participants cannot be a "Certificate Authority" in its true sense. This is why you should see "Let's Encrypt" simply as a cheap way to fake security. It is a US entity, which means it _must_ hand out all necessary keys to fake certificates to the US authorities _by law_. Now probably you can imagine why they are giving the certificates out for free. US authorities can compromise all of them - without any "open knowledge".
Wow, you packed a lot of fear, uncertainty and doubt (and some misinformation) into one paragraph. I'll leave it at that.
Joseph Tam <jtam.home@gmail.com>