Emails getting rejected from Gmail on Virtualmin/Webmin and CentOS

I have a CentOS 7 droplet that currently hosts 4 domains running Virtualmin/Webmin.

The dropled is named (which is one of the 4 domains). PTR record is updated correctly with the droplet IP.

BIND DNS Server module is disabled, as I am using the “Networking > Domains” panel provided by DO. Per each of my domains, I have configured DNS as follows:

A         @       *droplet ip*
A         mail    *droplet ip*
CNAME     www
CNAME     *
MX        5
TXT       @       "v=spf1 a mx ip4:*droplet ip* ?all"

Here are my /etc/hostname

And /etc/hosts

▽      server   localhost.localdomain   localhost   localhost4.localdomain4  localhost4

::1          server
::1             localhost.localdomain    localhost
::1             localhost6.localdomain6  localhost6

*droplet ip*

And /etc/resolv.conf

# Generated by NetworkManager

Finally, I have setup a forward from to my gmail account.

Here the issue comes: if I send a test email from my outlook account to I expect it to get it delivered to my gmail account. However, this is what I get back:

This is the mail system at host server.localdomain. 

I'm sorry to have to inform you that your message could not 
be 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 can 
delete your own text from the attached returned message. 

The mail system 

<> (expanded from <>): host[] said: 550-5.7.1 [*droplet ip*] 
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 for more 550 
5.7.1 information. r7si49844073wmg.47 - gsmtp (in reply to end of DATA 

What am I doing wrong?

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It sounds like your droplet’s name is not a FQDN (Fully Qualified Domain Name). If you rename your droplet to use a FQDN (such as, the PTR record would update for your automatically. Once that globally propagates, you would not longer get that error from gmail.

Hope it helps! Jason Colyer DigitalOcean Platform Support Lead