Is DNS MX Record Required For Email?

[Mark Andrews]

> Is it possible to by-pass the DNS lookup for email like it is for HTTP and 
> FTP? Is there something about the MX record in DNS that requires a 
> "User at DomainName.com" type address for it to work?
> 
> Here's why I ask.
> 
> I have a static, always-on IP address coming into my house. I run Web and 
> FTP servers on my PC.  They work fine, and have for a long time. My OS is 
> Windows NT 2000 Professional.
> 
> When I scan my ports from a remote machine I get what I expect, which is:
> 21 (FTP): Open
> 25 (SMTP): Open
> 80 (WWW): Open
> 110 (POP3): Open
> 143 (IMAP): Open
> 
> I only share data with people I do business with. I prefer to just use my IP 
> address instead of aliasing it with a domain name. (For these examples I'll 
> use "1.2.3.4", which is of course not my IP. But it's easier to type.) There 
> is no DNS entry for "1.2.3.4" anywhere.
> 
> "http://1.2.3.4" gets into my web server without a problem.
> "ftp 1.3.3.4" (DOS prompt) gets to my FTP folder without a problem.
> 
> But..., when I send an email to "User at 1.2.3.4" it fails. I have a mail 
> account with a Windows based ISP and am experimenting sending mail from it 
> to "User at 1.2.3.4". It doesn't work.
	
	Well to send email to a IP address the correct syntax is
	"user@[1.2.3.4]".
 
> I have my the mail server on my machine configured correctly. And have the 
> domain/accounts set up like they should be, including a "User at 1.2.3.4" 
> account.
> 
> Any thoughts/tips greatly appreciated. 
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org