Normally your ISP provides you the Numbers or it's picked up by your Modem then Router.
These Servers have been patched to guard against DNS poisoning, and are faster/more reliable than most ISP's DNS Servers.
http://www.opendns.com/solutions/overview/
And the fact that this did not work tells us what?
Your ISP, or wrong gMail settings.
Mine are...
Incoming imap.gmail.com (different for POP)
Port 993 Use SSL Password authentication
Outgoing smtp.gmail.com
username@gmail.com
Port 25 Use SSL Password authentication
.........
* The POP3 port for inbound emails is 110 (995 if you want to use secured POP3)
* And the IMAP port for inbound emails is 143 (993 if you want to use secured IMAP)
* The SMTP port for outbound emails is 25 or 2525 (465 or 587 if you want to use secured SMTP)