The importance of email
Email must be one of the most revolutionary things that the Internet has brought to the world. It allows fast communication between people at great distances. Sure, the same could be said about the telegraph or the telephone. However, email has some obvious advantages over those two.
Email can be sent from home - this is not true for using the telegraph. Because emails can be composed while offline, you can then connect to the Internet for a short while using your telephone line and send that message. This makes email cost effective.
One major advantage of the email is that the person doesn't have to be there to pick-up the message the moment you send it. My brother was visiting US and the email was the most convenient way to keep in touch. For me it wasn't so much of a wonder, but for my parents, especially for my mother, it was great. She was able to know so much about her son while he was away.
For those of us that are used to all this, email seems ordinary, but I can tell you: There's nothing ordinary about it when it comes to usefulness!
Web based email
The great thing about getting a hosting account is that in perhaps 99.9% of cases it comes with email capabilities. That means you can setup a certain number of email accounts. Each such account can have a certain size, meaning it can hold X MB of data.
Web based email is email capability, but with a twist: you can read/send emails using a web browser such as Internet Explorer, Mozilla (Netscape) etc.
This allows you to simply connect to the internet and, without the need of specialized software, log into your email account and read, reply, compose emails. If you've ever used a free email service like Hotmail, Yahoo Mail or the new Gmail you know exactly what I'm talking about.
A few programs are used to intermediate the access to the emails through a browser. Among the more common are NeoMail, Horde and Squirell Mail. Certainly, there are differences between them. Some swear that Squirell Mail is the best, others that Horde and others that NeoMail.
These preferences are usually 50% proof, 50% religion, as often is the case when it comes to software. For the average user however, besides the look, the functionality is similar.
Most hosts allow access to at least two such applications via the control panel. It doesn't cost them much because they're all developed for free by passionate people.
POP, IMAP, SMTP
Email however, can be managed in faster, more advanced ways. For that purpose certain email specific protocols were created. By using these protocols, certain programs provide you with an easier and faster way to read, store, delete and send emails.
Among the more known software are Outlook, Outlook Express, Eudora, Mozilla Thunderbird. My experience with Eudora is very limited. Reading about other people that loved Eudora I tried to use it, but, perhaps because I was coming from Outlook Express, I found it to be complicated in an unnecessary way. I never found the will to insist until I got used to it, so I went right back to Outlook Express.
Now however I'm using Mozilla Thunderbird, which many people recommend as a secure Outlook replacement. For anyone used to Outlook Express it should be pretty easy to make the switch.
For retrieving emails, the following protocols are the most common: POP (Post Office Protocol) and IMAP (Internet Message Access Protocol). I'll tell you from the start that my favorite is IMAP. I've used POP in the past until I learned about IMAP and found it much better.
POP is also known as POP3 because this is the most recent version of the POP
protocol (I know that's like saying Post Office Protocol protocol)
but I had no idea on how to express the idea. And now Idea and Idea... twice
in a row... am I tired or what? 
So, as I was saying... there is a small, but important difference between IMAP and POP. When using POP protocol, by default, the emails that are on the server are moved to the client machine (aka "your computer"). By that I mean they are copied on the client machine and deleted from the server. You do have however the option of setting things in your email software so that the emails remain on the server.
With IMAP, the emails are downloaded on the client machine, but by default they are not deleted from the server. This means that you can re-read those emails on any computer at a later time, by accessing them on your server. You're the one who decides when the emails will be deleted. I recommend you pay close attention when you're setting up your email accounts. After all, you only need to do a good job once and you're set for a long time to come.
I bet you'll say it doesn't much of a difference whether you keep emails on the server or not, but I can tell you that the difference is significant in certain situations. Say you are away in another town for a day or two. If you verify your email from another computer using POP "without the safety on", you'll have to save those emails on a disk for later reference, because they'll be gone from the server.
In addition to keeping the files on the server, I highly recommend that you keep an archive of all your important emails.
Now, a hosting server usually can understand (speak) both POP and IMAP. However, out of the two, I personally use IMAP.
POP and IMAP are used to retrieve and manage our emails, but to send emails another protocol is used: SMTP or Simple Mail Transport Protocol. In programs such as Outlook you can setup the SMTP server at a different address than the one used for IMAP (like the one given to you by your ISP).
However, SMTP is now a part of almost any hosting package. Not getting it would be a surprise. If your ISP didn't offer you a SMTP account to use, SMTP must come from your host, so make sure the host provides it.
Spam
Now, by reading the beginning of this article one might get the impression that email is all nice and dandy. Well... be amazed! People found a way to misuse this wonderful tool too! They invented spam.
What is spam? As strange as it might sound, spam is defined by different people in different ways. I guess it's not very wrong to say that each individual has his own definition for what spam is.
Basically though, spam is an unrequested commercial message. However, broader definitions exist, such as "any message that is unrequested".
I will not go any further though. Almost anyone can recognize spam when they see it, and all people agree: spam is annoying. It costs all of us time to select and delete emails that we know we don't care for.
To help us reduce this type of cost, certain tools were developed. One of the most well regarded and widely used is SpamAssasin. It is a mail filter that helps to identify spam.
Spam filters try to determine which emails are spam by using a set of rules. These rules are mostly based on "reading" the email and determining whether it contains spam-specific words/techniques. The suspected emails are then marked or separated. If you receive a lot of spam, a filter can be very helpful in dealing with it. There are people out there who are thrilled by spam filters; they find them to be life saviors.
Email and hosting
A respectable hosting package must include email capability. Email is such a basic service today that a website without email is almost inconceivable. One of the most basic reasons to register a domain and get hosting is to have an unique email address: This e-mail address is being protected from spambots. You need JavaScript enabled to view it. .
Now, email must work. And it must work great! Some emails are too important to be missed. That's why hosting must be reliable. If the server is down, email is down. People might send you emails that never make it into your inbox, and you can't reply to messages that you don't receive, right?
So much business is done via email nowadays that for some people having no downtime for their email service is even more important than having no downtime for their website.
Conclusion
Email and hosting go hand in hand. Website hosting is important, but considering that website hosting is usually intimately tied with email capability (or vice versa), the hosting company that you select for your website becomes twice as important. This shouldn't come as a surprise: quality, honest hosts are the key to quality email service.