In KMail, there are separate lists for "Identity" (meaning "From" address, signing info, etc.), the outgoing mail server and the incoming mail server. This is good since the three are not necessarily connected.

My particular use case: I travel between home and work with my laptop. Each time I switch locations, I need to use a different SMTP server. Kmail makes this easy enough, as I just need to tell it in the "Compose" dialog which outgoing server to use. Evolution makes this hard because I have to change this for every account I want to send email from, every time I travel. Oww.