This is a Good article of how it all works:
Evolution mail is an Open Source email project that you can use to host your own mail system.
http://www.gnome.org/projects/evolution/
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Get IT Done: Host your own e-mail server
by Jim Boyce | Mar 27, 2003 8:00:00 AM
Tags: E-mail servers, Get IT Done, e-mail, Jim Boyce, e-mail server, server
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Takeaway: Host your own e-mail server
E-mail is more pervasive these days than the business letter was just a couple of decades ago. Having a reliable e-mail server is crucial to most businesses. However, many companies—particularly smaller ones—have not taken the next step to host their own mail servers. Some rely on their local ISP to provide e-mail services, while others turn to Hotmail, Yahoo, or other global mail service providers. Hosting your own mail server offers some nice advantages, whether you need to support hundreds of users or just want to put in your own mail server in a small office. In this Daily Drill Down, I'll take you through the ins and outs of setting up your own mail server.
An e-mail server to call your own
Most national and local Internet service providers don’t offer a lot of features when it comes to their mail systems. The majority of them give you the ability to filter your messages so you can try to block all those annoying messages for herbal diet plans, debt consolidation, and hot stocks, not to mention all those unsolicited messages you wouldn’t want your dear old granny to see. But that’s about where the level of service ends. If you want features such as out-of-office replies, automatic responses, unlimited mailboxes, and mail forwarding, you need to take matters into your own hands and put in your own mail server.
You might think that putting in your own mail server means a big outlay in new equipment, expensive software, and time to manage it all. As long as you have an always-on, broadband Internet connection, however, it can be a snap. Because many of the mail server applications run on Windows 9x and other nonserver operating systems, you may not even need to change your existing systems. Even if you don’t have a dedicated Internet connection, you can still install a mail server that dials your ISP to send and receive messages.
What you do need, however, is an understanding of how e-mail messages get routed on the Internet, how to make those messages come and go through your server, what features to look for in a mail server, and then how to put it all together into a working package. Before I get into the nuts and bolts topics, let’s take a look at what you can expect from your own mail server.
What will you gain or lose?
One of the main things you’ll gain from setting up your own mail server is complete control over how many mailboxes you can have, how those mailboxes are set up, and how they work. Are you running into size limitations on your existing mail service? Does your current mailbox keep filling up or rejecting your messages because they are too large? No problem! When you own the mail server, you can do whatever you want. Go right ahead and send that 20 MB attachment to the remote office.
That brings up another important advantage that your own mail server can provide. You can extend the benefits to others, hosting accounts for other branches or even partners. That’s particularly nice if you’ve succeeded in securing a domain name for your company. The downside comes if your remote sites and business partners start to rely a little too much on their mail accounts. If your Internet connection goes down for a few days for reasons beyond your control, or your server suddenly develops a bad case of virus-of-the-week, you don’t want people calling at 2 A.M. to complain about it. I’ve been in the 24/7 support business and hated it. You will, too, if you get in that position. If you open your server to others, make sure they understand that they get what they pay for and should have a backup option, such as Hotmail or Yahoo. You should have a backup for your own e-mail account as well.
Autoresponders are another handy feature offered by many mail servers, and they're much like out-of-office replies. For example, maybe you have a document you want people to be able to obtain simply by sending a message to a specific account. A customer can send a message to fudge@yourdomain.whatever and get back a reply with your favorite fudge recipe. Businesses often use autoresponders to distribute information about products and services. Whether you manage services for a commercial venture or run a small home business, autoresponders might add a new way for you to interact with your customers.
Many mail servers offer features that make it easier to distribute mail to groups of people. While you can create distribution lists with any e-mail client, creating groups at the server lets anyone send mail to that group through a single e-mail address. Some mail servers give you the ability to send messages to group members in round-robin fashion. This means that each new message gets sent to a different person in the group. This is a great way to distribute messages evenly across the group, and it is typically used to distribute sales or support requests.
Keeping out spam is another potential benefit to hosting your own mail server. While you can create rules in your e-mail client to delete messages from specific senders, keeping out spam for several mail accounts can be a headache, particularly if your current service doesn’t give you any spam-blocking features. With antispamming built into the server, you can block mail from domains or specific senders for all accounts.
Many mail servers also provide built-in virus scanning or can use add-ins to scan messages coming and going through the server. You might use this in conjunction with client virus-scanning software to add another layer of security for your home network.
Laying the groundwork
To set up your own e-mail server and keep it working, you need some understanding of how e-mail gets routed across the Internet. Simple Mail Transport Protocol (SMTP) is the glue that binds Internet messaging. Mail servers use this protocol to communicate with one another, and e-mail clients use it to send messages. For example, let’s say I send a message to Uncle Ned asking for a copy of his pickled onion recipe. My mail program (let’s assume Outlook Express) connects to the mail server for my mail account using SMTP commands.
Through these commands, my message gets placed in the server’s outgoing mail queue. The server then looks at the address for the message to determine the destination. It queries the DNS to find the IP address of the mail server that serves that destination domain. My server then uses SMTP to communicate with the other server to deliver the message. If a network or server problem prevents the two servers from transferring the message, the message remains in the sending server’s outgoing queue for a specific period of time (the default is usually four days). The server periodically tries to resend the message, and if it can’t do so by the time the specified expiration period occurs, it returns the message to the sender with a nondelivery receipt (NDR).
When it comes time for Uncle Ned to retrieve the message, he has a handful of options. The most common is the POP3 protocol. When you connect to a mailbox on an ISP’s mail server, the mail program uses POP3 to retrieve the message. With POP3, messages are downloaded to your local computer, but you can optionally leave a copy of the messages on the server. This lets you also retrieve the messages from another computer, if needed.
IMAP is another protocol supported by many mail servers. With IMAP, the messages remain on the server and you access them live. You can read and delete messages from the server as well as create new ones. However, new messages are sent using SMTP rather than IMAP. IMAP is a good option when you need to access mail from more than one computer, because the mail is always available on the server instead of being downloaded to your computer—you don't have to worry about synchronizing mail stores on different computers. However, it does require a mail client, such as Outlook Express, Outlook, or Eudora, that supports IMAP accounts.
Some mail servers also support HTTP, the same protocol used to serve up Web pages. HTTP support lets you send and receive e-mail through your Web browser. Yahoo and Hotmail are two examples of services that provide HTTP-based e-mail, and Outlook Web Access (OWA) under Exchange Server also offers this capability. The main advantage to using HTTP is that you don’t need a dedicated e-mail client program but can instead rely on your Web browser to send and receive e-mail. This makes it easy to work with your messages from any computer.
Choosing the right software
I owned and operated an ISP for several years and used Microsoft Exchange Server to provide e-mail to our customers. As you may have guessed, I instinctively recommend Exchange Server for new e-mail servers. However, Exchange Server lists for just under $700 without any client licenses and just under $1,300 with five licenses, so that puts it out of range of most small businesses.
If Exchange Server seems like too much horsepower or too much money, there are lots of other good commercial, shareware, and even freeware mail server programs that range in price from free to a few hundred dollars. A search of popular download sites such as CNET Shareware.com, Tucows, and others will turn up a couple dozen e-mail server programs.
When you’re looking for a mail server to use in your business or home office, start by weeding out the ones that won’t run on your operating system. In most cases, programs designed to run on Windows NT or Wi