Cannot send an email to gmail

I followed this tutorial http://www.howtoforge.com/perfect-server-centos-6.4-x86_64-apache2-dovecot-ispconfig-3.

I can send an email from gmail to my domain but I cannot send an email from my domain to gmail

I got the following message back from gmail:

How can I solve this?

Thank you in advance

 

Did you go to the URL suggested in the reply?

 

Yes. But it is neither Bulk Sender nor Mail Forwarding.
I also checked for Black List IP. My IP does not in the black list.

 

Your system seems to use ipv6 for mail sending.
Have you checked that your server's name does resolve to it's ipv6 and the rdns for the ipv6 is set?

 

I'm a newbie with CentOS.
Could you guide me how to do rdns?

 

You can try

Code:

host -a your.servername.com

and

Code:

dig -x serverip

and

Code:

dig -x serveripv6

You see the configured ip addresses by typing

Code:

sudo ifconfig

 

You need a PTR-record for your ipv6 (http://rdns6.com/hostRecord) or just disable ipv6 in postfix whend sending mails to google (http://blog.schaal-24.de/?p=2900&lang=en)

 

Thanks Croydon and florian030.

Finally, I can make it work now by setting protocol to use only ipv4.