I have been screwing around with e-mail based product development work the last 5 years and so I have a fairly good grasp of how e-mails flow along the Internet.
Now that reminds me long ago in college I answered a paper about how e-mail flows on the net. I got it wrong. I thought that just like packets flow from hop to hop mails are stored at each hop. I started with spam control and now I also have a mail server. Basically an e-mail that is sent from point A to reach point B on the Internet has to pass through multiple routers the same way a web server is reached. But there are lot of differences. The primary concept is that of how DNS plays with it. A DNS record called the MX pointer is key here. For you to receive mail from the outside world a DNS record has to tell them that the domain you are hosting can be reached on such and such IP address. An MX record is not an IP address. It is a mapping between a domain name and another domain name whose A pointer points to the IP address. $ dig zoho.com mx will tell you. Or $ dig +short gmail.com mx Anyway the point is that for a mail server to function properly it should both send and receive mail traffic. A simple mail server is easily configured using any worthy UNIX operating system. It comes with stock sendmail, postfix, qmail, exim or whatever else. The popular solutions like Zarafa, Zimbra, Scalix, Kerio and so on are built on top of Postfix or sendmail or any such. I use postfix. It is far easier to be able to send mail out than to receive them as sending does not involve MX pointers. Only static IP that is not blacklisted is necessary. If you have that you can easily send mail that is received by most servers. In that regard you may check the popular blacklist sites like senderbase.org used by Ironport which hurt my customer a lot these days(I somehow fixed the issue) and blacklistcheck.org or some such thing. If you have a DHCP address like in a normal broadband then dont run a mailserver. You can only when you can authenticate against gmail and wish to use a smarthost to transmit and receive mail. Not much fun in running such a mail server. Now for how spam control works. I guess most of the technically minded clued in guys would have followed something about e-mail servers. Spam control falls into a technology area identified by Gartner and other MBA companies as e-mail security gateway solutions or network security in case you talk UTM as I wrote two days ago. It is about controlling unwanted mail at the gateway/network level. But just like virus scanning this can be done at the user mailbox level as well using simple Outlook rules. But almost in every case spam control is performed at the mail server. We will discuss that later. E-mails are sent and received using port 25 of TCP, port 587 called as submission port is used in certain cases where it is normally authenticated. And port 110 and 143 are used for POP3 and IMAP4 for downloading mails from mail server to mail clients like Outlook also called as MUA. mutt is the MUA I use in UNIX. Dovecot is the best server for this. It handles authentication for POP3 and IMAP and serves mail from mailboxes. There are other secure variants that use SSL and SMTP auth is another topic for mail relay authentication. But for sure authentication is done during mail download to identify the user's mailbox. For mail relaying/sending it is not a must as the authentication is performed by the IP address as it belongs to the accepted network of Postfix. This is where a VPN is very helpful as you can belong to the local network segment from anywhere in the world by using OpenVPN and connecting to the company's mail server. If not you can use the submission port 587 and do SMTP auth to send mail. I have not configured this so far. -Girish -- Gayatri Hitech http://gayatri-hitech.com _______________________________________________ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
