Mailer delivery circuit

Mail delivery involves the following subsystems:

1. Sendmail: Used for sending mails to nodes outside the LTNB, and for delivering incoming mails to the user's mailbox in /var/spool/mail Communicates with the following entities:
   1. A local browser: typically, a netscape browser in one of the classrooms, configured to browse mail via IMAP. The local browser only contacts sendmail for sending mail, not for browsing received mail.
   2. The IMP Web-to-mail gateway, which allows remote browsers to access our mail. No local configuration of the local browser is necessary, making it easy to access mail this way from anywhere on the world (Cybercafé, at work, from a friend's computer, ...). IMP only contacts sendmail for sending mail, not for browsing received mail.
   3. Remote peers, i.e. mail transfer agents at other institutions. They contact us when they send mail to us, and we contact them
   4. Writes delivered mail to user's system mailbox in /var/spool/mail
2. Imap: Used for browsing received mail, and for organizing it into folders.

   Communicates with the following entities:

   1. Reads user's new mail from his system mailbox in /var/spool/mail and moves it over to the mbox file in his homedirectory.
   2. A local browser: typically, a netscape browser in one of the classrooms, configured to browse mail via IMAP. Local browser only contact imap for browsing received mail/organizing it into folders, not for sending it.
   3. The IMP Web-to-mail gateway, which allows remote browsers to access our mail. No local configuration of the local browser is necessary, making it easy to access mail this way from anywhere on the world (Cybercafé, at work, from a friend's computer, ...). IMP only contact imap for browsing received mail/organizing it into folders, not for sending it.
3. Local browser: A netscape browser in the classroom

   Communicates with the following entities:

   1. Imap for browsing received mail & organizing it into folders
   2. Sendmail for sending mail
4. IMP: Web-to-mail gateway

   Communicates with the following entities:

   1. Imap for browsing received mail & organizing it into folders
   2. Sendmail for sending mail
   3. Remote browser, for whom it acts as a Web server
5. /var/spool/mail: System mailbox

   Is accessed by the following entities:

   1. Sendmail delivers mail to here
   2. Imap reads mail from here, and clears it
6. Remote browser: Netscape browser running off-site

   Communicates with the following entities:

   1. Connects to IMP, which acts as a webserver
7. DNS: Domain Name Service

   Communicates with the following entities:

   1. Supplies addresses of remote mailer destinations to sendmail
   2. Supplies address of our own mail servers to remote senders

Needed cisco ports

• TCP port 25 from/to ltnb0 to deliver mails outside/receive mail from outside.
• TCP port 25 to ltnb10 (our backup mail server), so that he can receive mail if ltnb0 is down.
• TCP port 25 to tuxtux, for mail to Arbed.
• TCP ports 143, 110, so that users outside can access their mail directly through imap or pop.
• TCP ports 80 and 443, so that users outside can access their mail via IMP.