To get the server name, you need to have a conversation. With whom? With either your Internet Service Provider (for a home or small business account), or, for a work or school account, the Network Administrator of that system.
Here's how the conversation should go. Roughly.
YOUHi! I want to get the name of the server
for my email account with you.
THEM
OK. It's pop.gobingo.com. (for example)
YOU
Pop dot gobingo dot com?
What does that mean?
THEM
I don't know. But it's the
name of the server.
YOU
Oh...and it's a POP server,
Right?...Post Office Protocol.
THEM
That's right! You really know your stuff.
YOU
Thanks!
Note: It's not possible to use the external mail feature to check messages in another Yahoo!7 Mail account that has been set up for POP access.