This HOWTO is dedicated to all the off-line linux users/servers ... You got a group, or organization, and you want all your members to have a contact (email) address, without paying for the 24/24 direct line or for the email accounts ... Or you got a internal network - with a masq'd server and you want to give all the users using it a email address, you could use this way to do it. I personally am using it to give my users & members of a demogroup all a e-mail account without being 24/24 online; since it is a non-commercial demogroup - and we don't got THAT much money to pay a direct line with instant email access - and different ip's. Everybody got a email address, even when they don't got internet access. The ones with internet access can receive their mail on their personal email address - viavia the system described below. Your users can still send mail as they used to do, since - your system will hold the mail queue from the users. The only thing what should be changed for the users - is that they add their "email address" wether (described below) it is the method with the subject line, or with the header "to" ...
Not every (free) mailservice is happy when you are going to distribute mail to other users, or putting up an anonymous mail server, so, please try to contact your mailserver administrator before "just doing it".
It is slower than a direct 24/24 connection, since your server will need to get online before it will process the mail.
It needs a administrative force to administrate the "mailrouting" and to add the user ... you will need work with it ! - it is not that automatic. (well - i made it "semi-automatic" with my server :) you could try it as well).
Bandwidth and space is needed when you got many users - on the mailserver you are working on ... and sure - when they send files - you need to have enough space on it !.
All mail will be transferred into "one step" - so - the last mail received on your server will be last sent to the recipient. "first in - first out".
In the first method (to:) there is no prob with the usernames - but in the second "cheaper" method - users can't put in a subject line, since that one will be used to send the mail to the recipient. Many users forget to use the "subject" ... - or they will need to know it clearly.
If you poll enough for your mail, (for example 4 times a day) - the mail will be sure be delivered to as from a recipient the least every 6hrs. So the processing will go a little smoother.
you CAN use it as a "online" mail server as well :) since it will poll for it's mail for every XX minutes. but - when you are online - why using another server ? and not asking your own domain for your own server ? (dough).
method 'A' - now called "(m(A))". The "mailsystem" will look to the header, and will see to the "to:" line. This is the best way, since it are "real email addresses". You will need another account on some server *AND* you need a DNS (MX) entry (your own domain for instance). If the system administrator wants to help you with that, then there will be no problem !. The system administrator will need to reroute ALL mail sent to your (MX) maildomain -> to your account !. This will take some time for him to do it :) so be really nice to him :)) Thanks to my system administrator (Fred) i got my maildomain and the user- services of my "free" demogroup. It can be a DNS entry costs something, what you will need to consider to take it or not.
method 'B' - now called "(m(B))". The "mailsystem" looks to the subject line, and will forward to the user indicated into the subject line. If the user is not found, it will bounce a mail back. This will need a pop server with only one useraccount, and don't need your own DNS or you don't need to be nice to your system- administrator who arranges you the mail address :). You can use a public mailserver, as well your own mailserver or a private one. You can even sacrifice your own email address for it :). I used this approach as first what worked for me for over a year now ... I know this is sloppy, but, i ain't telling you need to use this way, so don't shoot ME - since i'm only offering you some solutions to your mail problems :) - you could use method A what isn't that sloppy !