I believe they are right. Here is a little more information.
We moved last year and received a different range of public IPs from our ISP. Our old publix MX record was 166.90.163.134. Our new address as of last November is 66.118.31.132. We only have two customers that send us email and we do not receive it for about 24 hours. I have verified over and over again with the guys who host our dns record that our MX record is the correct IP address. But here is what one of the customers has to say about the problem:
Right after I sent this I was finally able to catch the problem as it was happening. I noticed that all of the sudden yakko.advantatech.com started reporting 166.90.163.34 instead of the previous address I mentioned (see the ping results below).
After flushing the DNS cache it started reporting the correct address again. Would you have any idea why we would suddenly start getting the wrong address for this? I’ll keep checking from my end.
C:\>ping yakko.advantatech.com
Pinging yakko.advantatech.com [166.90.163.34] with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 166.90.163.34:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms