Yesterday, we found that the application can not send mail successfully; the performance of the module using email feature is also very bad. I suspect it caused by that the mail server host name can not be resolved in the application server.
I executed the following command
host <mail server host name>
It shows a strange IP. It means it can not properly resolve the mail server host name
Then I execute the command below.
man host
The output tells me to resort to /etc/resolv.conf
open it with
vi /etc/resolv.conf
The context is as following:
nameserver <name server 1>
nameserver <name server 2>
update the config with correct DNS server IP.
Everything is OK.
P.S. It seems that the ping and host commands are different. For some host name, I can ping it but I can not host it.