i would like to make my own mini version of yahoo mail
im not talking about all the web interface,
but strictly, the email portion

(i will do the administration, and the user will use a client, like eudora, or MS OutLaw

(a user can have mail, but is NOT a user, on the machine (has no account) )

im using redhat 8.0 and sendmail 8.12.8

This is a very ugly undertaking. First, if you want to become an Email service provider for others you have some architectural choices to make.

1) Do you supply SMTP (outbound) or only inbound.
2) Do you want to set this up as a forwarding server, or do you actually want to store the Email for them, until the user hits POP3 or IMAP to get to that mail.

To supply SMTP without local user accounts, look into EXIM. It has LDAP capabilities.
http://www.exim.org/
To supply POP3 and/or IMAP service, you should look into the Cyrus packages.
http://asg.web.cmu.edu/cyrus/

[edit] Oh and to make the users not have to be system accounts - look into OpenLDAP
http://www.openldap.org/

1) Do you supply SMTP (outbound) or only inbound.
2) Do you want to set this up as a forwarding server, or do you actually want to store the Email for them, until the user hits POP3 or IMAP to get to that mail.

1) i can email, using a winders client to/from anywhere,
via an account on my linux box....
(i seems to have smtp, and pop3 going, so it seems)
2) i want to store it, untill the user wants their mail

I feel really bad for not noticing this thread. Sorry, lenlutz, to leave you hanging.

1) I do supply SMTP outbound support for remote users through OpenLDAP authentication features in Exim.

2) This server is primarily a mail storage server, where people leave mail on it (if they use IMAP or SquirrelMail) or store it on their local machines (Outlook, Eudora or Mozilla POP3).

3) Make sure that you use a setting that does not allow relay without Authentication, and it is a bit of a task, but I found Exim to be much easier to make do this than sendmail. If you have smtp that allows relay, your ISP may shut you down as a spam-site.

4) IMAP and/or POP3 can be used in conjuction with a storage until read, or even store after read.

Did you check out neomail? It is a perl based server that you install locally and others can use your box as a mail server.

Also, alot of my mail from linux is getting bounced back now due to spam blocking, even though my mail is not spam. yahoo bounces, and corp's bounce as well. How do you plan on getting around this?

there is also a way to set this up with courier-imap, postfix and mysql

or

courier-imap, postfix and ldap.

check out the courier-imap page. there is a guide to setting it up both ways, i think it requires postfix 2.x

ahh i found it:

http://www.high5.net/howto/

that's the courier-imap + mysql tutorial to setup virtual domains and users (email accounts without system acconts).

now to have your clients use something like Eudora or Outlook to connect without becomming an open mail relay is another issue. you'll have to throw in more software to do pop3 authentication. SASL comes to mind but i've never used it or tried to. the easier way out is to setup webmail.

i like squirrel mail or imp

http://www.horde.org