Move MX record to its own subdomain

[link2xt]

No description provided.

[hpk42]

changelog entry is missing.

[hpk42]

hum, i'd say it's a BREAKING change, in that updating to this change requires changing DNS/a chatmail server's setup.
therefore, also please provide a reason for this change.

[feld]

What is the purpose of the MX record here anyway? Everything will fall back to the A/AAAA record so it's really unnecessary unless you have a more complicated architecture and want multiple MX records with priorities

[link2xt]

@feld

Everything will fall back to the A/AAAA record so it's really unnecessary unless you have a more complicated architecture and want multiple MX records with priorities.

The reason for this PR was that I wanted to point MX record to a different IP addresses that have port 25 open and DNAT to the real server IP address. So even when you have a single MX record a little more flexibility is useful when you have trouble opening port 25.

[hpk42]

Please provide a reason for this change. i can guess but it's not clear to me, sorry.
Also, would the letsencrypt certs not need to be adapted for "mx.maildomain"?

[missytake]

Please provide a reason for this change. i can guess but it's not clear to me, sorry. Also, would the letsencrypt certs not need to be adapted for "mx.maildomain"?

One reason is that we can then add proxy VPSs for IMAP+SMTP usage only, but not as MX. This makes it okay if a proxy is slightly fragile, as we know that the IP caches of Delta Chat can handle it, even if other SMTP servers might not.