Mailing list using sendmail
At the moment we have a self-driven mailing list that operates in the following way:
1) We have a POP mailbox, firstname.lastname@example.org which is hosted at our ISP.
2) Our Linux server at work polls this address with fetchmail, and puts the mail into the "clients" homedir ("clients" is a user on the Linux server).
3) A .forward file resides in the "clients" homedir, which then forwards all mail to an alias called "clientlist".
4) In /etc/aliases, this sendmail alias "clientlist" is then defined to contain all the client email addresses.
Yes, there are some major flaws with this - I know. However, we are running into a brick wall installing mailman or majordomo. The above-mentioned procedure works very well, but has one major flaw - anyone can send mail to our clients by just sending an email to that address. As far as I know, there is a way to setup a procmail filter to solve this problem though.
Basically what I need to know is:
1) How can we set up a filter to only allow one specific email address to send mail to our mailing list address. (Remember, the POP mailbox itself doesnt reside on our server, it's at the ISP. We only poll it with fetchmail and then bounce it to the aliases defined in sendmail).
2) What other solutions are there? Apart from mailman and majordomo.
Would really appreciate your help :)