We have investigated a couple of instances of this problem, and both were caused by the computer supplying the wrong IP Address for the ISP’s email server, rather than looking up the Domain Name.

Please do a “ping” to your ISP’s email server to find its IP Address.  The following example pings “mail.bigpond.com.au” and discovers that its IP address is 144.140.90.10

C:\Documents and Settings\Support>ping mail.bigpond.com.au

Pinging mail.bigpond.com.au [144.140.90.10] with 32 bytes of data:

Reply from 144.140.90.10: bytes=32 time=22ms TTL=249
Reply from 144.140.90.10: bytes=32 time=21ms TTL=249
Reply from 144.140.90.10: bytes=32 time=20ms TTL=249
Reply from 144.140.90.10: bytes=32 time=20ms TTL=249

Ping statistics for 144.140.90.10:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 20ms, Maximum = 22ms, Average = 20ms

Please edit your  Email Account settings to replace the mail server domain name with the IP Address just discovered as shown below. Save, and try checking for mail.

Note that the above is a work-around, and not a proper long-term fix for the problem.  By using the domain name, the ISP is able to transfer the email server to another IP address and then simply change the Domain Name mapping to send all the clients to the new server.  If or when that happens, this workaround will stop working and the above procedure will need to be repeated.

We were unable to determine why these users’ computers stopped looking up the email server’s Domain name but suspect it may have been a side effect of a virus scanning application, or perhaps malicious software they downloaded accidentally from somewhere.