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Tue 23 May 2006
Send Email From Anywhere
Category : Technology/EmailAnywhere.txt
It used to be that you could send email from literally anywhere, once you've turned on your own SMTP server. However, some mail servers (at hotmail or AOL, etc.) have increasingly hit back by implementing a filter that rejects mail originating from a dynamic IP address (which is all of us trying to send mail from a broadband line).
Tagging someone as a spammer simply because he's trying to send mail from a dynamic address strikes me as being too simplistic.
We all have our favourite reasons why we want to be able to send mail out our PowerBooks from wherever we are and whenever we want. Most ISPs have rules that block you from sending mail out their server if you're not on their network. So, if you're roaming around with your PowerBook, you're often out of luck. That's why being able to send mail out our own Postfix-enabled mail server on our PowerBooks became such a god-send ... for a while.
Plus, if we're now able to run a full-fledged mail server off a simple broadband line with a dynamic IP address, and since it's cheap, powerful, easy to do, and yet effective, then why shouldn't we be allowed to do it?
But now, when we're trying to send mail out of a broadband line (see the two orange arrows, below, denoting the case of a MacBook sending mail out localhost, and the case of a Mac-based mail server on a broadband line), we're likely to get rejected by, say, 30% of the mail servers out there, as denoted by the Dell-type, IT-managed servers in the picture, below :
It's like we've found a way to go two steps forward and now we're being pushed one step back. So what's a nice PowerBook to do?
This is the setup I've been using. I've taken care to choose an ISP to run my server on that doesn't block any of the well known ports (25, 110, 143, 993 and 995 for mail and 80, 8080, and 443 for web, plus the other ports for SSH and FTP, etc), and who doesn't have any restriction on using their SMTP server as a smart host. They may require authentication and they may require SSL, but that doesn't matter as long as they allow my mail to be relayed out through it using my own mail server.
So this is what happens when I'm roaming around with my PowerBook. I connect back to my server and relay mail through it, which will in turn relay it through my ISP's smtp server (the blue arrows in the picture, above). Because it's relayed through the ISP's server, it looks like a static IP address to the receiving mail servers, and that practically ensures that my mail won't get rejected by mail servers implementing those petty rules.
So how does that beat simply going through the ISP server in the first place?
Well, my mail server is a full-fledged mail server, so it receives mail and implements both the POP and IMAP services besides sending mail.
Secondly, I've set it up to allow my PowerBook (as well as any of the other users I've registered on it) to relay mail through it from anywhere I happen to be - so long as I authenticate with it. And I've set it to listen on two other ports (2525 and 52525), in case I'm on a network whose control-obsessed administrators block port 25, the send-mail port. (Surely, networks are there to be used?). Plus, I've turned on SSL, to encrypt the communication between the mail client and the server, including the password exchange.
So this has worked pretty well for me and I continue to run my mail server over a dynamic IP address ... until such time when the admins decide to respond with another block?