[Novalug] email server with dynamic IP

Ed T. Toton III bones@necrobones.net
Mon Jan 8 16:56:12 EST 2007


Thus spake Craig Pennington:

> Also, IIRC an MX should not be a CNAME, so make sure you're pointing to 
> an A record.
>
> And lastly, to make explicit what Nick's above configuration says 
> implicitly, I'd make sure you've got a backup MX so that in the times 
> when your home net goes down you don't lose mail. I use ZoneEdit for 
> backup MX, but I imagine there are plenty of good ones out there.

Heh, I'm still catching up on mail, so sorry for another late reply. :)

Yes, that's correct. There are many mail servers out there that won't 
follow a CNAME used in the MX records. You need an A record here. However, 
since dyndns creates A records with a short TTL (60 seconds), you can use 
this directly, like this:

 	IN	MX	10 sample.dnsalias.net.

(example with an account of 'sample' and their 'dnsalias.net' domain option)

If you really must have your MX use a hostname within your domain, then 
you need to script something up to modify your zone based on what your new 
IP is (which could in turn be pulled from resolving your dyndns address if 
it's being updated by a router or something where you don't otherwise have 
easy access to the IP) and host the DNS yourself.

As someone else pointed out, you may have difficulty sending from your 
dynamic IP if the recipient sites are blocking mail based on the dynamic 
IP blacklists (and even if they're not using the blacklists directly, it 
may also increase the spamminess of your messages in filtering). An easy 
fix is to have your mail server route all outbound mail through your ISP's 
mail servers.

Of course this whole discussion assumes your ISP is not blocking inbound 
port 25 traffic. Otherwise you're out of luck.


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- Ed T. Toton III, RHCE --|-- www.necrobones.com -- ed.toton.org -
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