Error 550-5.7.1 when trying to send emails to gmail.com

==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.2
- Linux/BSD distribution name and version: Ubuntu 14.04
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): Apache2
- Manage mail accounts with iRedAdmin-Pro? No
- Related log if you're reporting an issue:
====

Hello dear community.

I have really strange problem. So far i used to send and receive emails without any problem, but today i have problem.

My problem is only with gmail.com. There is the error that i receive when i try to send an email to account at gmail.com.

Action: failed
Status: 5.7.1
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.1 [77.85.204.32] The IP address sending this
    message does not have a PTR 550-5.7.1 record setup. As a policy, Gmail does
    not accept messages from IPs 550-5.7.1 with missing PTR records. Please
    visit 550-5.7.1
    https://support.google.com/mail/answer/81126#authentication for more 550
    5.7.1 information. d4si4817657wjn.111 - gsmtp

My reverse DNS is pointing to mail.vivashost.com with CNAME. Where my mistake can be ?

Thanks in advance!