linux (debian) problem with sending mail

I had some issues with sending mail through my mail server. It is debian distribution, and some users got error mails return to them. This is what they got back:

This is the mail system at host sportikus.kif.hr.
I'm sorry to have to inform you that your message could notbe delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You candelete your own text from the attached returned message.
                   The mail system
<xxxxxx@brugger.at>: host mail.brugger.at[213.229.60.100] said:    550-Inconsistent or no rDNS record for 161.53.51.3 (see RFC1912 2.1)    550-http://www.ietf.org/rfc/rfc1912.txt 550-Reverse DNS record and matching    forward entry must exist. 550 => wrong configuration at sending server    161.53.51.3 (in reply to RCPT TO command)

This was obviously error in dns configuration, specifically in reverse dns. So I edited hosts.rev changed serial number (just +1) and added one line to the end of that file:

3       PTR   sportikus.kif.hr.

 and reloaded the configuration with

rndc reload

Note that number 3 is the ip address of the server.

And that was it! :)