Email password - noob question

[#1]

This is a really basic question.
If I set up an email account in Outlook or Outlook Express it requires a password - obviously.
Now the bit I am not sure about.
If the email account is with another provider so that the pop3 is user@1and1.co.uk for example and the outgoing server is relay.plus.net does the PlusNet part use the password or is that only for receiving emails

[#2]

No password on relay.plus.net - only for the incoming pop3 server.

[#3]

Thanks - now goes away and hides in a corner for not knowing that