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General Settings

Go to System Setup > Mail Relay > General Settings to configure the mail firewall appliance settings for the postfix mail relay. The table below describes each of the settings.





The fully qualified hostname of SpamTitan Gateway.

Fallback SMTP relay(s):

This is an optional list of relay hosts for SMTP destinations that can't be found, or that are unreachable. The default value for this setting is blank/empty and this is the recommended setting for most installations.


Use this feature with caution if sending outbound email through SpamTitan Gateway.

Outbound mail that can not be delivered will also be sent via the fallback relay which will likely result in the mail being rejected.

By default, mail is returned to the sender when a destination is not found and delivery is deferred when a destination is unreachable. The fallback relays must be SMTP destinations.

Specify a domain, host, host:port, [host]:port, [address] or [address]:port; the form [host] turns off MX lookups.

If you specify multiple SMTP destinations, SpamTitan will try them in the specified order. To prevent mailer loops between MX hosts and fall-back hosts, SpamTitan will not use the fallback relays for destinations that it is MX host for (assuming DNS lookup is turned on).


If relaying outbound mail through SpamTitan and a remote mail server is unreachable, then the fallback relay will be tried.

Greeting Banner:

The text that follows the 220 status code in the SMTP greeting banner. The default value is $myhostname ESMTP $mail_name, where $hostname expands to the fully qualified hostname of the appliance and $mail_name expands to Postfix.

Sender address for verification probes:

The sender address to use in address verification probes (default: postmaster). Specify an empty value or <> if you want to use the null sender address.


Some websites reject mail from <> even though RFCs require that such addresses be accepted.

SMTP Helo Name:

The hostname to send in the SMTP HELO or EHLO command. The default value is the machine hostname ($myhostname). Specify a hostname or IP address.

Proxy/NAT network addresses:

Specifies all network addresses that the appliance receives mail on by way of a proxy or network address translation unit. You must specify your proxy/NAT addresses when your system is a backup MX host for other domains. Otherwise, mail delivery loops may occur when the primary MX host is down.

This setting should be left at the default (empty) for most setups.

Domain verification method:

Select a method for domain verification (default: Disabled). Domains can be verified by either MX record or email. Domains must be verified before you can pass your mail through SpamTitan. See Domain Verification.

Max number of recipients per message:

The maximum number of recipients that the SMTP server accepts per message delivery request (default 1000).

Max message size:

This setting applies to all incoming mails. If your backend server has a limitation on message sizes, set this to the same or a lower limit. A reasonable maximum setting is 20 or 40 MB. Specify 0 for unlimited (default).

Queue Lifetime:

The maximum time a message is queued for delivery before it is sent back as undeliverable (default: 5 days).

Defer Queue Notification:

The time after which the sender receives the message headers of mail that is still queued (default: 0 hours).