Centos – Sendmail – Relaying denied (state 14)

TLS just enables encryption on the smtp session and doesn't directly affect whether or not Postfix will be allowed to relay a message.

The relaying denied message occurs because the smtpd_recipient_restrictions rules was not matched. One of those conditions must be fulfilled to allow the message to go through:

smtpd_recipient_restrictions =
    permit_sasl_authenticated
    check_recipient_access hash:/etc/postfix/filtered_domains
    permit_mynetworks
    reject_unauth_destination

To explain those rules:

permit_sasl_authenticated

permits authenticated senders through SASL. This will be necessary to authenticate users outside of your network which are normally blocked.

check_recipient_access

This will cause postfix to look in /etc/postfix/filtered_domains for rules based on the recipient address. (Judging by the file name on the file name, it is probably just blocking specific domains... Check to see if gmail.com is listed in there?)

permit_mynetworks

This will permit hosts by IP address that match IP ranges specified in $mynetworks. In the main.cf you posted, $mynetworks was set to 127.0.0.1, so it will only relay emails generated by the server itself.

Based on that configuration, your mail client will need to use SMTP Authentication before being allowed to relay messages. I'm not sure what database SASL is using. That is specified in /usr/lib/sasl2/smtpd.conf Presumably it also uses the same database as your virtual mailboxes, so you should be able enable SMTP authentication in your mail client and be all set.

As the page states, the HELO is not why your server is listed.

IP Address 93.190.139.208 is listed in the CBL. It appears to be infected with a spam sending trojan or proxy.

is why your server is listed. You'll need to figure out why it's being flagged as such and correct it.

Changing how your server identifies itself in the HELO is specific to the SMTP server that you're running. Can you give us a clue?

EDIT

Ok, got it. You have a couple of problems based on your edit:

1. CBL thinks you're spamming but offers no details on what exactly they're flagging you on.

2. It looks like atlantamail.com is rejecting your email because it can't validate the name your SMTP server is giving in the HELO command. You'll need to figure out where in Postfix to set the outgoing FQDN in the HELO and set it to something legitimate, such as hostname.mypublicdomain.com. If you send and receive email on the same server then it's easiest to set the FQDN to match your MX record and then you can create an SPF record that authorizes your MX to send email for your domain. None of these will guaranteee that your email will be accepted but will help.