CSF Possibly Blocking Gmail

[ZeroNine]

First off, I am not sure where to post this questions so I do apologize if this is in the wrong forum.

I been using Gmail to receive my emails from all my websites for a few years now.
Couple days ago I noticed that I didn't receive any emails so I checked settings in Gmail and saw "Connection Error. Mail from this account has not been retrieved since Apr 2" for all of my email accounts. I then viewed details and then saw Connection Error. Server returned error "We were unable to locate the other domain. Please contact your other provider."

What makes this so weird is that, this has NEVER happened before for years I been using gmail.
I opened up outlook, set up the same email accounts to check to see if I was able to pull all the incoming emails and sure enough it is working perfectly.

I am suspecting that maybe Gmail IP is being blocked by the server so Gmail is no longer able to pull the emails.
(I am using POP3)

I should note that I am however able to send emails of all the accounts through Gmail without no problem.
I have csf and mod security installed. I checked blocked ip addresses and saw no blocked ips that looked like from google.

Can anybody help me resolve this?
Is there some other way for me to determine what is wrong?

[Sergio]

Turn CSF off and check if gmail can reach your server, if so, then CSF is blocking gmail in some way.

To check if there is a Google IP blocked, then make a list of all the IPs blocked in your server and using a script like IPNetInfo from www.nirsoft.net check them all and see what IP belongs to gmail.

Sergio

[ZeroNine]

Thank you Sergio,
I turned off CSF and sure enough it all worked.
So I downloaded IPNetInfo as suggested and loaded up all the deny ips list into the application however, none of the ips turned up as a google. Since turning off CSF did work, is there somewhere else I should be looking to figure out where or how its being blocked?

[Sergio]

Have you checked IP V6? Google is working with V6 and it could be that you have not opened email ports for IP V6.

Sergio

[ZeroNine]

No I have not. I'm a bit of a noob when it comes to this.
Where and how should I look for this?

[Sergio]

In CSF configuration, go to the IP 6 tcp in/out and add there the email ports and left any other in therr.
If you already have ports in there, just add the email ones, hope that helps.

Sergio

[ZeroNine]

Hello Sergio,
I added the pop ports 110 and smtp port 465 in ip6 but its still not working.
I wonder what else it can be...

Thank you for you help regardless.

[Sergio]

Hello Sergio,
I added the pop ports 110 and smtp port 465 in ip6 but its still not working.
I wonder what else it can be...

Thank you for you help regardless.

According to google:
"Open ports 995 and 465, the Gmail ports for receiving in POP and sending in SMTP. "
"Check that POP3S (or IMAPS) is allowed at your selected security level. Those are the well known service names for ports 995 or 993. "

Try opening ports 993 and 995 open in IP V6.

[Sergio]

ZeroNine,
check in your CSF firewall if you are blocking the IP range 74.125.0.0/16, if so, delete that IPs and see if gmail works now.

[ZeroNine]

Thank you Sergio!!
Everything is fine now.
I didn't want to reply too fast because I had to be sure it was working properly.