Raoulduke's link is probably for newer versions of Eudora. Anything that runs on an '000 or an '020 isn't going to be capable of talking to Google directly, because Google absolutely mandates SSL encryption.
Google has further gone out of their way to separate (and by default, disallow) clients that it thinks aren't secure enough, even if they do support all of the right security and encryption standards.
Another way around it is, as techknight mentioned, to use another mail host that allows you to make the decision to use "insecure" standards.
The insecurity of these standards is that if you use plain IMAP or POP3 without SSL or TLS encryption, your user name and password (and all your mail) are transmitted over the wire in clear, human-readable text. With an updated server, it shouldn't really cause any problems to allow these standards on a modern mail system. (I've considered it for the local LAN on my server, but that'll be a problem for later.)
Another possibility is to use telnet with a shell account and pine/alpine/mutt, etc, but at that point you're not really using "the Mac" for email as much as using it as a telnet client and doing your mail on a remote computer of some variety.
Google has further gone out of their way to separate (and by default, disallow) clients that it thinks aren't secure enough, even if they do support all of the right security and encryption standards.
Another way around it is, as techknight mentioned, to use another mail host that allows you to make the decision to use "insecure" standards.
The insecurity of these standards is that if you use plain IMAP or POP3 without SSL or TLS encryption, your user name and password (and all your mail) are transmitted over the wire in clear, human-readable text. With an updated server, it shouldn't really cause any problems to allow these standards on a modern mail system. (I've considered it for the local LAN on my server, but that'll be a problem for later.)
Another possibility is to use telnet with a shell account and pine/alpine/mutt, etc, but at that point you're not really using "the Mac" for email as much as using it as a telnet client and doing your mail on a remote computer of some variety.