Most Unix/Linux Operating Systems come with Sendmail already preinstalled and ready for you to use.

The biggest problem you will face configuring Sendmail is deciding how to layout your mail services architecture.

It doesn't matter if your machine is a server or a workstation; Sendmail is probably installed the same way on each machine. This means that if someone had the right privileges they could configure their workstation to be a mail server. The same configuration files control Sendmail regardless of how you're running your machine.

Taking the time to carefully decide how you want mail services to flow will save you time and grief. Once you've decided on how you want things to work then all you need to look for are the commands and configuration options that will implement your architecture.

Although the goal of Sendmail might be to just deliver the mail doing so is not as easy as it sounds. Some people think that Sendmail is a complex mail system. In reality it is not complex but it is highly configurable. The number of options that you have at your disposal just makes it appear to be a hard system to learn.

What can Sendmail do? It can be used to read and write e-mail messages. Its main job though is to route messages to other users on your machine or to other users on other computers. The other computer can be on your network or on someone else's network. The other user can even be on a different type of network than yours. You might be on a TCP/IP network and the other person could be using DECNet. As long as Sendmail has a way to make a connection to the other machine it has a reasonably good chance of accomplishing its goal of delivering the mail.

What systems does Sendmail have to interact with? Sendmail interfaces with the /etc/hosts file, DNS, name server switch file, NIS, NIS+, LDAP, NFS, TCP/IP, Hesoid, Bitnet, DECNet, UUCP, routing of mail, masquerading, user defined preferences, vacation responses, aliases, mailing lists, security settings and a whole raft of timeout settings. It may need to interface with some of these different software components just to send a message from one user to another user.

What do you need to be concerned with while setting up your e-mail infrastructure? Which machines will the user use to receive e-mail? Which machines will the user use to send e-mail? Will the disks on the mail host machine be locally attached? Will the end user NFS mount the mail directory from the mail host machine back to their workstation? Will you setup alias names for some or all of your users? Will you have mailing lists? Will you allow your users to forward mail messages? Will you configure outbound message routing? Will you allow all of your hosts to be autonomous? Will you provide POP3 or IMAP client services for your users? How will you backup the mail files to protect yourself against disk crashes? There's a lot to consider when you're designing an enterprise wide e-mail system whether you're using Sendmail or any other program that provides similar services. Do the planning upfront and you'll soon have a system that won't require much attention. On a side note, Sendmail itself does not have any mechanism for POP or IMAP services. If you desire those features you will have to install and maintain more software.

In order for Sendmail to interact with different networks Sendmail may need to change the message so it can be delivered.

Computer systems usually have standards or specifications that software needs to adhere to for things to work properly.

Sendmail could look at an e-mail message and simply decide that it doesn't meet the standards for the network that it is being asked to route a message onto and simply reject the message.

Instead, Sendmail takes the opposite approach and tries to shape the message to ensure that the things that need to be there are there, and the things that don't need to be there, aren't there. The goal of Sendmail is to try to deliver the mail, not try to find ways to avoid having to delivery the mail.

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