Debian 10 MX hostname issue

Question

I am facing an issue where every single site like intodns, dnsstuff, mx toolbox is reporting that i have 2 issues. Namely:

1. Reverse DNS does not contain the hostname
2. Reverse DNS does not match SMTP Banner

However, as you can see in my cloudflare settings, the MX does not use any weird underscores at all.

Even my systemctl, does not show this weird underscore hostname that these MX are reporting.

My VPS provider also does not have this underscore as can be seen in this screenshot

I tried using grep to search for this weird "underscore hostname" but grep does not yield any results at all. This is the command i use.

grep -rnw --exclude-dir={boot,dev,lib,media,mnt,proc,root,run,sys,/tmp,tmpfs,var} '/' -e '_dc-mx.d51280fd8d88'

Answer 1

You are showing the MX record for a .com domain. But the unusual hostname containing the underscore is returned when querying MX records for an .sg domain.

If you want to have these host names valid and matching between those domains, check the MX records of both domains and set them to the host name you want to use (and have setup a PTR record for).

When you are done, verify:

1. both domains have the desired name(s) in their MX records
2. those desired mail server names resolve to your servers IPs in forward direction
3. their IPs point back to the server name when resolved in reverse direction