The SMTP proxy can be used as a mail relay. A mail relay is an SMTP server configured in such a way that it allows specific users, user groups, or hosts to relay (i.e., send) emails through it to domains that are not local.
Note – Some of the features on this tab are not available with BasicGuard subscription.
An upstream host is a host that forwards email to you, e.g., your ISP or external MX. If you get inbound email from static upstream hosts, it is necessary that you enter the hosts here. Otherwise spam protection will not work properly.
To add an upstream host either click the Plus icon or the Folder icon for drag-and-drop from the Networks object list. How to add a definition is explained on the Definitions & Users > Network Definitions > Network Definitions page. If you would like to only allow upstream hosts select the checkbox Allow upstream/relay hosts only. SMTP access will then be limited to the defined upstream hosts. Upstream hosts can authenticate to get relaying rights. Click Apply to save your settings.
SMTP clients can authenticate to get relaying privileges. Select the checkbox Allow authenticated relaying and specify the users and user groups that should be able to use this feature. How to add users is explained on the Definitions & Users > Users & Groups > Users page. Click Apply to save your settings.
Note – If the checkbox Allow upstream/relay hosts only is enabled then Authenticated Relay does only work when the sending host is configured as upstream/relay host.
Mail relaying can also be enabled host-based. If your local mail server or mail clients should be able to use the SMTP proxy as a mail relay, you need to add the networks and hosts which should be able to send mail through the relay to the Allowed hosts/networks box. The networks and hosts listed are allowed to send messages to any addresses. How to add a definition is explained on the Definitions & Users > Network Definitions > Network Definitions page.
Caution – It is extremely important not to select Any in the Allowed hosts/networks box, because this would result in an open relay, allowing anyone on the Internet to send messages through the SMTP proxy. Spammers will quickly recognize this, leading to massive email traffic. In the worst case, you will be listed on 3rd party spammer blacklists. In most configurations, the only hosts that should be allowed to relay mail are the mail servers in your network.
Click Apply to save your settings.
Here you can define hosts and networks that shall be blocked by the SMTP proxy. Click Apply to save your settings.
When this option is enabled, also messages sent by either authenticated or host-based relays will be scanned for malicious content. If there are many outgoing mails, turning this option off can improve your performance. Click Apply to save your settings.