More and more Mailservers drop your connection if your Mailserver (the SMTP Proxy) do not announce itself with a valid hostname within the HELO/EHLO line.

Endian Firewall uses it's own known hostname in order to announce to foreign Mailservers. Sometimes this hostname is not publicly valid within the global DNS.

If that is the case, you can configure another custom hostname within "Proxy > SMTP > Advanced > SMTP Helo Name".
You can also use a numeric ip address if you put it within brackets (e.g. [192.192.192.192]).

If you see appearing "Mail for xxx loops back to myself" within your log file, you probably configured a custom SMTP HELO name which however is the same as the hostname of your internal Mailserver to which the incoming Mail should be forwardet.

In that case your internal Mailserver would receive an SMTP connection whose HELO line from the SMTP Proxy claims to have as hostname the same as the internal Mailserver itself uses. For the internal Mailserver this seems to receive Mail from itself.

Solutions:

• Change the hostname on your internal Mailserver
• Create a new publicly valid A Record within your DNS zone which also points to Endian Firewall and use this hostname as HELO line within the SMTP Proxy.
• Use the numeric IP Address of your uplink as HELO line.