[Exim] failed to find hostname from IP problem

Hi,

I am using exim 3.36 on FreeBSD. Everything works perfectly but I noticed
that I am getting the following error message when trying to send a message
using SMTP:

550 relaying to webmaster@somehost prohibited by administrator (failed to
find host name from IP address)

This is very annoying, since I have explicitly allowed relaying for the
specified host, but due to lack of DNS communication the IP cannot be
resolved. Is there a way to disable this feature (resolving IPs to names)? I
read almost the entire exim documentation but could not find anything on
that topic.

Any help would be appreciated!