Mailblocks

To reduce the amount of spam sent to our users, we refuse mail from hosts that seem to be configured incorrectly (and in many cases have already been abused to send spam).

In other words, if mail of yours has been rejected, this is likely due to a misconfiguration of your mail system (though, unfortunately, we cannot completely rule out false positives).

For help, please forward the error messages you have received to your technical staff/your service provider and postmaster@dbai.tuwien.ac.at (who is excluded from the blocking setup and will be able to help).

For other ways to contact us, please refer to our address page or email postmaster@dbai.tuwien.ac.at.

Technically, we block:

1. Hosts that lack reverse DNS, that is, hosts whose IP address does not correspond to a name (which is a configuration error on your side). This is described in RFC 2505. (You can find a copy here.)

   The error message in that case will read "Client host rejected: cannot find your hostname" or similiar.

2. Hosts that have reverse DNS, but whose name does not resolve to the IP address actually used.

3. Hosts which identify themself (using HELO or EHLO) with a hostname which does not resolve.

4. Mails from outside our institute addressed to

   • ... some of the local aliases, particularized: aicom, bb, dbstud, education, intpract, matrix and staff. For the latter you can use mitarbeiter instead which isn't blocked.

   • ... recipients outside our institute. In that case please request email authentication on that page.

In all of these cases, please contact your site administrator.

Some documents which describe this requirements:

• RFC 1123: Requirements for Internet Hosts -- Application and Support
• RFC 1912: Common DNS Operational and Configuration Errors
• RFC 2505: Anti-Spam Recommendations for SMTP MTAs
• RFC 2821: Simple Mail Transfer Protocol