Controlling the routing of address verification probes

By default, Postfix sends address verification probe messages via the same route as regular mail, because that normally produces the most accurate result. It's no good to verify a local address by connecting to your own SMTP port; that just triggers all kinds of mailer loop alarms. The same is true for any destination that your machine is best MX host for: hidden domains, virtual domains, etc.

However, some sites have a complex infrastructure where mail is not sent directly to the Internet, but is instead given to an intermediate relayhost. This is a problem for address verification, because remote Internet addresses can be verified only when Postfix can access remote destinations directly.

For this reason, Postfix allows you to override the routing parameters when it delivers an address verification probe message.

First, the address_verify_relayhost parameter allows you to override the relayhost setting, and the address_verify_transport_maps parameter allows you to override the transport_maps setting. The address_verify_sender_dependent_relayhost_maps parameter does the same for sender-dependent relayhost selection.

Second, each address class is given its own address verification version of the message delivery transport, as shown in the table below. Address classes are defined in the ADDRESS_CLASS_README file.

Domain list	Regular transport	Verify transport
mydestination	local_transport	address_verify_local_transport
virtual_alias_domains	(not applicable)	(not applicable)
virtual_mailbox_domains	virtual_transport	address_verify_virtual_transport
relay_domains	relay_transport	address_verify_relay_transport
(not applicable)	default_transport	address_verify_default_transport

By default, the parameters that control delivery of address probes have the same value as the parameters that control normal mail delivery.