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I've found that my 2 domain providers both prevent me from putting my static IP address in the MX record for my domains.

But let's say my IP is 71.222.111.33.

If I open up port 25 on my Wifi router and have a mail server listening for incoming connections, what would prevent someone from successfully sending an email to warren@71.222.111.33 ?

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The email server they are using wouldn't accept it. –  Ramhound Aug 17 '12 at 11:46
    
If email systems are structured in a way that effectively every email can be wiretapped, because it has to go through some corporation's server, then email itself is a worthless technology. –  Warren Aug 17 '12 at 12:02
    
Actually an interesting question that I'd like to see answered as well. –  invert Aug 17 '12 at 12:04
    
Your static IP (as, you own it), or your providers static IP which you are leasing? –  Hennes Sep 9 '13 at 15:27

3 Answers 3

Have you asked your ISP if they permit home e-mail or other servers? In many cases the ISP will simply block any traffic to certain ports like 25. As the traffic passes their router(s), it is either dropped or blocked in some way. Same for HTTP and HTTPS and many other protocols. If you by a "business" or "commercial" package from them, then the traffic passes without issue. But you are now paying a much higher price.

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As explained in section 4.1.3 of the STMP specification (PFC5321#4.1.3), you have to use an address literal if the host has no name. The correct syntax would be:

warren@[71.222.111.33]

As by the standard, this is supposed to work. I tested it, and it works fine with Thunderbird and Postfix.

But there are email clients and/or mail servers that will choke on this syntax (basically because they don't respect the standard). For example, the email provider WEB.DE marks that address as invalid.

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Bottom line: Either switch providers or get a cheap VPS. All of the problems described here and in your other question will go away if you get a VPS. –  Dennis Aug 17 '12 at 12:14
    
I've confirmed that Comcast and Yahoo mail servers reject this format. I've already paid for web hosting for a couple years with Network Solutions, whose provided email is utterly useless. The pop3/imap servers don't even work. –  Warren Aug 17 '12 at 13:23
    
I mean a VPS with root access, not some pre-configured one. You can configure the VPS as you wish, just as you would do with your home computer. It's what I'm doing, and it's working very well for me. –  Dennis Aug 17 '12 at 15:16
    
Oh well, the money's spent already. I'll keep VPS in mind for next time. –  Warren Aug 17 '12 at 15:29

This is not a direct answer to your question, however it may be a solution to your problem.

If your domain registrar allows you to change the Nameserver records for your domains (which all good registrars should) you can use a 3rd party DNS management provider to set your static IP as an MX record.

I have used ZoneEdit for many years.

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