So lets start:
- Most ISPs don't provide "forwarding" service when you decide to leave them for the competition.
If you're not planning on switching ISPs right now, you can give your friends and family a heads up. Start by sending a message to everyone you know has your existing e-mail address. Then setup a mail client rule to forward all messages to your new account on GMail (my preference) or another service.
For added convenience, setup another rule to reply to those messages with a notice that your e-mail address has changed. You have a much longer buffer period for your friends to update their address (or ignore). You can even take it one step further and change the message to say "I no longer check this account, if you want me to receive this message, send it to "firstname.lastname@example.org".
- You're no longer tethered to your ISPs service.
ISPs know that the fact that you being hooked into their e-mail service is something that may prevent you from shopping around for a better deal. If you're not tethered to their exclusive services, you can leave for that better deal (assuming you live in an area that actually has broadband competition!). I have close friends that kept their AOL dial-up subscription for years because the pain of giving up their @aol address was too much (they've all moved on now, thankfully ... that, or I've just stopped having friends who would use AOL).
- Your passwords aren't sent in plain text.
Your e-mail account is the window into your world. Most people use their "ISP" e-mail account like they use their home phone. They provide it to those with whom they engage in transactions with (such as the Credit Card Company or The Bank).
If you make a habit of using open access points, or public access points, that silly mail client of yours is probably sending your password plain-text every 5 minutes. If someone gets that password, they simply have to collect some e-mail from you to determine who you do business with, visit the site, and use the "Forgot my Password" link, where most services will conveniently send your new password via e-mail.
Make sure you pick a service that encrypts your ID and Password by default. GMail requires an encrypted connection on their web site, and if you use their free POP access, it'll be encrypted there too.
I'm dumbfounded by the fact that so many ISPs do not even allow encrypted authentication on their e-mail servers.
- You can take your e-mail with you.
Yes, it's web mail, so if you want to check it from a location other than home, you probably can (assuming the internet connection your using isn't blocking web mail). In addition, with GMail you can access your e-mail in the same manner you're already likely used to ... via Thunderbird, Outlook, Outlook Express or your favorite mail client at no additional charge.
Yahoo! also offers POP3 mail, however, at the time of this writing, you'll have to subscribe to their premium service.
- You can send e-mail when you're not on the same network.
This is similar in nature to the above, and may already apply to your ISP e-mail. Some ISPs only allow you to send mail if you're connected via a set of IP Addresses that they own. This means when you're using an open WiFi Network, you can receive mail just fine, but cannot send it.
Most ISPs have addressed this limitation, but if yours hasn't, you'll now have the ability to send and receive via either your web based client, or your own local client.
- You may find the Web mail features to be better than your mail client.
I have both a GMail and Yahoo! mail account that I regularly monitor. As far as GMail is concerned, I'd rather use GMail than Thunderbird. It filters spam well, it integrates with their instant messenger client (as does Yahoo!), it allows for lightning fast searching of my old mail, and it redefines the way I work with e-mail by grouping messages in conversations and allowing me to apply labels.
Plus it's just dead simple to use. Not that I'm confounded by the "intricacies" of Thunderbird, but I find I'm more efficient using Web Mail.
- You will probably get more space for your mountains of mail.
This was the initial reason many people switched to GMail. They offered you 2GB of server side storage for mail (Indeed, some people even use it as a backup service).
- You now have that backup you keep meaning to do.
This comes with a caveat. If you aren't using both a local client and the web client, you're actually in worse shape than if you had only the local client and failed to backup. At least you'd still have the drive or computer that failed if you wanted to pay for costly recovery services. If Yahoo! or GMail loses your mail, you're stuck.
That said, if you use a local client regularly (and you're leaving your mail on the remote server), you now have redundancy. A lost drive does not mean that all of your e-mail is gone.
- Mobile E-Mail Access may be easier and less costly.
Of course, this always depends on who you choose as your e-mail service provider. For me, accessing my GMail account on my lousy Motorola E815's sorry excuse for a Web Browser is actually quite painless. They did mobile e-mail right, and it shows. It's easier for me to get into their service, check my mail, and get out than it is to use the kludgey POP3 client. And since my cell phone provider requires that I purchase the software to even check e-mail via my mobile phone, it costs less.
- SPAM and Malware are handled better.
Maybe you'll be a little more careful with this new account and not put it on your MySpace profile, or give it to every company that asks for it. You're starting fresh, give it only to trusted sources. Set up more than one account or use services like Mailinator for disposable e-mail addresses.
In addition, because Google or Yahoo! know about *all* of the spam their receiving, you may find (as I have) that their spam filtering far exceeds what even the most sophisticated of mail clients can pull off. Sure, your ISP may have server-side spam filtering also, but they probably don't have the user base that Google or Yahoo! Mail does.
In addition, most Web mail services scan all attachments for viruses (typically only when you use the Web interface). If you've been lax on your Anti-virus updating, this may save you.