Reverse lookup mx records and cnames

[schnitzelmeister at gmail.com]

Thanks for this.
Do you mind if I just confirm this to triple check?

If I have an A record for mail.provider.com pointed at 10.1.2.3, and I
have mail.customer.com pointed at 10.1.2.3, then it is completely okay
for the results of a dig -x 10.1.2.3 to only return mail.provider.com,
and not mail.customer.com?