We are having on and off mail problems. We have a mail server (Exchange 2000) in our domain that is receiving mail from an other mail server in the domain of our Headquarters. Our primary mail address is in the HQ domain and mail send to that address is forwarded to our Exchange server.
This worked for a long time with no problems.
Now we are getting messages that mail is being rejected with the following NDR:
#5.5.0 smtp;550 all relevant MX records point to non-existent hosts
When they try two minutes later the mail goes through without problems.
Where do I have to start looking for configuration errors? It puzzles me that it is working 99% of the time and 1% not. Configuration is either right or wrong...or is it???