for SMTP server theres hmail (http://www.hmailserver.com/) a free opensource email server. apart from that you could always log the keystrokes to a file with a simple encryption (a=b, b=c ect)
edit: didn't see you wanted a public one. I assume you meant one that anyone can access from the web.However, you could just make an email account with a free provider that offers smtp access. such as Gmail or HotPOP.
edit: didn't see you wanted a public one. I assume you meant one that anyone can access from the web.However, you could just make an email account with a free provider that offers smtp access. such as Gmail or HotPOP.