Setting your default address in cPanel – why its better to use :fail: instead of :blackhole:

Posted on November 11, 2007
Filed Under Configuring Email in cPanel, cPanel Web Hosting, Exim mail server, Mail Server administration | Leave a Comment

What does using :fail: no such address here for default address do?

This setting bounces unrouted email back to the sending address without it being processed by our mail server. This is better than :blackhole: because using the blackhole setting causes the mail server to accept and process the email before sending it to null. Fail on the other hand causes the email to be rejected (bounced) before it is accepted by the mail server. This prevents abuse of resources. This is also useful for other mail servers because it lets them know (from the bounced email) that the emails being sent are to non-existent addresses and the mail server administrators can then more easily detect and prevent abuse of their own services by spammers.

Why bounce unrouted email? Why not just accept it?

Experience will show you over time that unrouted mail is the preferred method of spamming. And the same experience will show you that spam is sent in great numbers, absolutely millions of spam emails are sent around the Internet daily. Spammers also use software to automatically generate random email addresses to single domains in large numbers.

Accepting unrouted email is the friend of spammers since they don’t have to guess or know what email accounts you have set up, they can send spam to any address for your domain and it will be accepted and delivered to whatever address you set as the default address.

Rejecting unrouted email is the enemy of spammers since they can send spam to any address at your domain but it will not be accepted unless they match an email address that exists (i.e. one that you have created in your control panel).

What alternatives are there for dealing with unrouted email?

You can use Forwarders to handle mail sent to non-existent email addresses. For instance, if you wanted to accept mail for user @ when you have not set up a mail account in that name, you can create a forwarder for that address to send the mail on to an address that does exist (and that does not have to be a mail address in your hosting account, it could be a mail address at your ISP for instance). This method maintains protection against unrouted spam email and still allows you to accept mail to certain addresses for which you do not want to create a separate account for.

A huge word of caution though, whatever address you set as the default address should really have a quota limit set as substantial amounts of spam can fill your quota. Filling your quota (where you have left the default address with an unlimited quota for instance) will stop your hosting from working because you … literally have no space left.




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