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Error when receiving a message

The error message ‘Client host rejected: cannot find your hostname’ is displayed to the sender if his provider has configured the IP addresses of his mail server incorrectly. Emails with incorrectly configured IP addresses are rejected by FireStorm.
The sender must contact his provider and ask his provider to correctly configure the IP addresses according to RFC guidelines section 2.1. Further information can be found in the following Wikipedia entry.

To avoid this error message, the reverse entry of an IP must match the domain name. This can be checked with the two commands nslookup [IP-des-Mailservers] and ping [DOMAIN] as shown in the following example.

Here is an example how the entries should look like. The IP 188.40.219.18 points to sr101.firestorm.ch. If this domain is pinged, the correct IP address is returned again.