Email Service that Can Be Used from Mac OS 9 Desktop Client?

[mac57]

I seem to be unable to find a desktop email client for Mac OS 9 that will interact successfully with modern POP3/SMTP, and even IMAP, email servers. My Mac OS 9 install comes with Microsoft Outlook Express, and I have also tried the built in email client in Netscape 4.7 and several others. The result is pretty much the same. I can receive and read email, but I cannot send it.

I am guessing that there is some new security protocol or exchange that these older email clients simply don't support, and which today's email servers demand.

Hence, is there an email service out there on the net that is friendly to older email clients?

Thanks!