Musings from a small IPP

It’s a mailhost, really!

by on Feb.11, 2010, under E-Mail hosting, Operations

Things have changed a lot in the 30 years I’ve been doing e-mail systems.  In those first heady days, establishing a transport fabric was hard work, and getting a message through over a mixture of uucp, decnet, snads, and arpa protocols a miracle of managing complexity, and co-operaion.  Now in February 2010 I reject 92% of the messages offered for my customers.  Strangely few of these rejections result in contacts from customers or their contacts  about false rejections — far more contacts relate to the SPAM we’re still letting through.  This week though I’ve had 2 contacts about mail getting rejected.  Both have the same underlying cause — the sending machine is not credible as a legitimate mailhost.

So what makes a credible mailhost?

  1. Mailhosts have fixed IP addresses
  2. Reverse DNS (when you look up the name associated with the IP address) gives a ‘real’ hostname, not a DHCP pool name.  For instance if I look up a host which has an IP address of I would be looking for a name more like ‘‘ than ‘
  3. The DNS lookup loop is complete.  That means that the name I get from looking up your IP address should look up in turn, and get me back to the IP address I started with.

None of this is even remotely rocket science.  As a mathematician might say, they are necessary, but not sufficient  to establish credibility.  Failing this test makes your server look like a virus-infected spam-bot.

If you’re trapped with a service provider who will not give you a fixed address or good reverse DNS then you have to either use the provider’s mail service for your outgoing messages, or a 3rd party who can offer a mail-submit service (such as we do).  Ultimately of course you should change provider to one which will provide the infrastructure you need to do the job you want to do.


Comments are closed.

Looking for something?

Use the form below to search the site:

Still not finding what you're looking for? Drop a comment on a post or contact us so we can take care of it!

Visit our friends!

A few highly recommended friends...