[gentoo-user] Technical imap mail question

[walt]

My ISP recently started offering imap email service in addition to
the pop3/smtp servers they've always had, so I decided to try it.

I was surprised to see that they recommend using a different smtp
server name when setting up my mail client, and they even offer the
option of using port 587 instead of 465 if I prefer it.

Why would I use a different smtp server if I'm now using imap?  I use
smtp to send mail, and imap to read it, right?  Why not use the same
smtp server in either case?

(The different server names actually resolve to the same IP address, so
the distinction seems to be more theoretical than real, but the theory
is what puzzles me.)

Thanks.