Recipient blacklisted by the Reverse DNS test - ORF Forums

I'm receiving this error in the log file:

Recipient blacklisted by the Reverse DNS test (no DNS MX or A/CNAME record for domain "remoteperformance.com").

However, when I do an nslookup on the email server, the server appears to have an MX record.

remoteperformance.com MX preference = 10, mail exchanger = mx.remoteperformance.com
mx.remoteperformance.com internet address = 64.26.60.153

Any ideas?

Perhaps because the rDNS record for that ip doesn't match the domain.

Reverse DNS for 64.26.60.153
Location: United States [City: Chicago, Illinois]

Preparation:
The reverse DNS entry for an IP is found by reversing the IP, adding it to "in-addr.arpa", and looking up the PTR record.
So, the reverse DNS entry for 64.26.60.153 is found by looking up the PTR record for
153.60.26.64.in-addr.arpa.
All DNS requests start by asking the root servers, and they let us know what to do next.
See How Reverse DNS Lookups Work for more information.

How I am searching:
Asking c.root-servers.net for 153.60.26.64.in-addr.arpa PTR record:
c.root-servers.net says to go to v.arin.net. (zone: 64.in-addr.arpa.)
Asking v.arin.net. for 153.60.26.64.in-addr.arpa PTR record:
v.arin.net [63.243.194.2] says to go to ns.siteprotect.com. (zone: 60.26.64.in-addr.arpa.)
Asking ns.siteprotect.com. for 153.60.26.64.in-addr.arpa PTR record: Reports mx0.mfg.onr.siteprotect.com. [from 64.26.0.23]

Answer:
64.26.60.153 PTR record: mx0.mfg.onr.siteprotect.com. [TTL 14400s] [A=64.26.60.153]

@MikeG
I thought the Reverse DNS test in ORF only looked for an MX or A record to exists (or only a MX record if that option is checked). I didn't think the PTR record was checked on this test. Am I wrong?

@Krisztian
No, this is not a local domain. It is a domain owned by a customer of ours.

I did nslookup on the same server, but this is now the second time I've had a weird DNS issue. I think one of my internal DNS server is having problems.

Thanks for the assistance.