The situation when the SMTP module receives a message from a remote system and then sends that message to some other host is called relaying.
To avoid Server abuse, some relay restrictions can be specified.
Relay to any IP Address: See the Protection chapter for the information about this setting. If the Nobody option is selected, relaying is still possible for authenticated users.
Relay to Client IP Addresses: See the Protection chapter for the information about this setting.
Relay to Hosts We Backup: This option allows the SMTP module to relay messages to any domain, if the MX records for that domain includes this CommuniGate Pro Server name (its Main Domain name) as a back-up mail relay.
Accept Wakeups: This option tells the SMTP module to accept ETRN commands and wake-up E-mail messages either from anybody, or only from the hosts included into the Client IP Addresses list, or from no host at all. Since the ATRN command, unlike ETRN, requires authentication, the ATRN command is always accepted from any address.
Hold Mail for Domains: When the SMTP module builds a queue for one of the domains (hosts) listed in this field, it immediately places that queue "on hold", waiting for the ETRN/ATRN command or any other external action that releases that queue. This method should be used for the sites that receive mail via your server, and that want to receive it only when they issue the ETRN/ATRN command. The specified names can contain a wildcard - the asterisk (*) symbol.
You may want to send messages for some of your CommuniGate Pro Domains via Local IP Addresses assigned to those Domains. See the Domain Settings section for more details.
If a message is to be delivered to the hostName host via a particular 18.104.22.168 Local IP Address, the message is not placed into the hostName SMTP queue. Instead, the Server places it into the @22.214.171.124|hostName SMTP queue.
This technique allows the Server to process messages from different Domains independently. If the IP Address of one of your Domains is blacklisted by remote hosts (because that Domain users have abused the mail system), messages to the same remote hosts from other Domains will not be delayed or rejected.
If the hostname name is included into the Hold Mail for Domains list, the Server never adds the @126.96.36.199| prefix, so all messages to that host are always enqueued into a single queue, and that queue can be used with the ATRN command.
The ETRN command releases not only the hostname queue, but all hostName queues wi