Quick question regarding Reverse DNS Record

I hope i'm in the right spot to ask this.

I recently got my ISP to provide me with a few reverse dns records for some mail servers. I've done this many times and never had any concerns about them working, but this time the results I get back when I test make me wonder if they were set up right, or more likely, that I am not understanding the protocol, and my googlefu is not working on this subject.

Is this an acceptable reverse dns record?

1.2.3.4.in-addr.arpa. 12345 IN PTR mail.acme.com.2.3.4.in-addr.arpa.

Thanks everyone.