Here is a shortcut to the protocol selection sheet when adding a new email account in Mail in Mavericks.

When adding other email accounts in Mail (in 10.9 Mavericks, I don’t know about earlier versions) hold down the Option key to turn the Create button into a Next button instead. This saves you the trouble of entering a fake email address to get to the sheet where you can select the protocol type.

[crarko adds: This goes back at least as far as Snow Leopard (where the button changed to Continue), but new users may find it helpful information.]

Source: Mac OSX Hints