Domains occasionally do not resolve

Occasionally a client contacts me to tell me that something "is down". They tell me that they see "domain cannot be resolved" message. I even asked them to do a ping or nslookup and it said that it could not find DNS entry.

The strange thing is that sometimes this happens to the example.com but webmail.example.com or john.example.com would be working fine and vise-versa. Other domains hosted on the same server would resolve no problem on the client's computer.

Usually this goes back to normal after a few hours or days. I don't see what could be causing this...

This has happened several times to two clients. They live in the same city, but don't know each other. They are on diffierent ISPs. It happened at different times.

Server config:
Linux 2.6.10-1.771_FC2 #1 Mon Mar 28 00:50:14 EST 2005 i686 athlon i386 GNU/Linux
Plesk 7.5.3
bind 9.2.3-13

 

 

 

 

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