Retrieve email error message on iphone 3gs
Since you did NOT specify the email type (server) lets use some generic methods to find out if the server is responding.
You can use something called 


  Ping


an IP address or hostname in the Terminal for Mac OS X

What Ping does is it send a signal to the server (IP address) and check for respond. So if the server is alive it will respond. That will however not say if they have specific problem on the server.

To do that open your Terminal in Utilities.

Type: 


  ping [-Options] ip or hostname


Usage: Ping's an IP-address or a hostname (which can be used to troubleshoot connection problems to another computer or a server).

Options

-c (num)    Stop after sending and receiving  number of packets.

-f  Flood ping: Flood ping, output packets as fast as they come back or 100 times per second.

-i     Wait for  seconds between sending each packet.

Example
ping 127.0.0.1  Ping your own computer (localhost)
ping -c 10 google.se    Ping google.se and stop after 10 sent and received packages.

Quick tip: If you're using ping and the response keeps coming in without stopping. Hold down "Ctrl" and hit "Z" (Ctrl+Z) to abort.