I run web and mail on one linode 512. It's a bit of a stretch but it does work.
You need an MTA (mail transfer agent) to send mail to and receive mail from the Internet. Postfix seems to be the most popular these days and it's not so hard to configure.
You need an IMAP server to let you download, read, and file your own mail. Dovecot, Courier, and Cyrus are popular. Cyrus is really aimed at big setups so maybe you should forget that one.
You will likely want spamassassin to catch spam. It's a memory hog but it does its job well.
You might want to do some reading at
http://library.linode.com/email