Every "co.uk" domain I send mail from bounces when trying to send to my address, jason@wickedmoon.com, on my dedicated RaQ4i hosted with rackshack.net. I've tried this with at least a dozen business contacts and friends who all have co.uk email accounts and domains, with the same result - email bounces back with a message similar to "Senders address does not exist".

Now Rackshack say this is an "unfortunate positive side effect" of using sendmail. That the host from which the email is sent should be responsible enough to maintain proper DNS records. Unfortunately the bottom line is email across many different networks is not getting through and puts a dampener on my idea of running an email service.

I wondered if this was a known quirk with sendmail on the RaQ? Is it just Rackshack? Is sendmail configured differently on the RaQ? As I've never experienced this problem before on the many hosts I've been with over the past 4 or 5 years. Is it fixable?

This maybe a mail relay problem. In the control panel, you must specify the acceptable relays. You may have already put co.uk in the relay list, but if the senders domain does not resolve you will not be able to send mail. The only way around this is to put the IP address in of the sending host. Also, you can open relay to all hosts and use POP before SMTP for security if putting in IPs is unreasonable.

Cobalt's install of sendmail has pretty scrict mail relay settings -- which is good and bad. If this is a major problem, you may look into Qmail, which has a few more options.


I had a similar problem with a client who used thier own dial-up server behind a coporate firewall -- their IP never got resolved, so they could not send mail. Putting in the first part of their IP followed by a ".", eg.
XXX.
permitted all connections from this host and solved the problem.

Huck, I just went through this with Rackshack and after a week of going round and round, between rackshack and cobalt we got this sorted out and it now works. I'll probably need to get into your control panel and look around. Email me if you want me to take a peek.

Captnroger.....

My email is working fine now ... dorokusai was having the problem, but thanks for your help. I am interested though in what the problem was and how you resolved it?

My investigations of the maillogs showed that certain IPs were not getting resolved properly. As a result, the sendmail anti-relay filters would not allow mail to be sent through the server.

I am not sure if the failed DNS lookups are due to Rackshack's DNS, which I use, or a more subtle problem with sendmail or both.

My solution was to open the server up a bit more to allow my clients to get in and use the POP before SMTP security settings. This seems to work pretty well. For a completely generic solution, you would basically allow all hosts to relay and rely on POP before SMTP, but this means if POP before SMTP was exploited, you would have an open-relay.

What did you have to do? And is this a general sendmail problem or a problem with Cobalts admin interface and how it sets up the access and host-relay files?