There are some :
There are some variants of access to mail and for the each one its own way to use proxy servers.
Web mail - is a mailbox with web interface. An example for such mail are Hotmail, Mail, Yahoo! Mail etc. It is enough to have access in Internet and a browser to use such mailboxes. In this case both getting and sending mail will be anonymous if you adjust your browser's proxy settings.
To get or send mail via POP3 / SMTP servers you can use the web interface. The web interface is a gateway which gives you access to POP3 to a server through your browser.
In this case for anonymous mail check/sending will be enough to set a proxy server in your browser.
You can also use remailer for anonymous mail sending . Remailer is mostly like the web mail. However there are also essential differences:
Since working with remailer you use a browser, it also possible to use an anonymous proxy server to connect to the remailer (double anonymity : anonymous proxy + remailer ).
If you want to hide your IP address from a mail server during reception of mail, it not a problem. There is a function of "mail gathering" in many free mail systems. So if you specify one mailbox to collect mail from the others mail servers, it will connect to the mail the specified servers and download letters. And you can get these letters from it later.
It's a bit more complicated to use mailing programs because they are not able to work through proxy.
There are 2 ways to decide this problem:
Go back to proxy FAQ