Returnenvelope Channel Option

Blank envelope return addresses
The  channel option takes a bitmask argument.

Bit 0 (value = 1) controls whether or not return notifications generated by the MTA  are written with a blank envelope address or with the  address of the local postmaster. Setting the bit forces the use of the local postmaster address, clearing the bit forces the use of a blank addresses. Note that the use of a blank address is mandated by RFC 1123. However, some systems do not handle blank envelope from address properly and may require the use of this option.

Bit 1 (value = 2) controls whether or not the MTA replaces all blank envelope addresses with the address of the local postmaster. Again, this is used to accomodate incompliant systems that don&#x27;t conform to RFC 821, RFC 822, or RFC 1123.

Bit 2 (value = 4) controls whether or not the MTA checks that any (non-empty) envelope From address matches (rewrites to) an MTA channel.

Setting bit 3 (value = 8) is equivalent to setting the  channel option: it controls whether or not the MTA checks that the domain in the envelope From address resolves in the DNS. That is, setting the bit causes the MTA to require that a DNS entry can be found corresponding to the domain in the envelope From address; but the type of DNS entry does not matter.

Setting bit 4 (value = 16) causes the MTA to enforce that if the envelope From address claims a local domain name, the envelope From address must correspond to a user address (user alias).

Bit 5 (value = 32) modifies the effect of bit 3 (value 8). When bits 3 and 5 are both set (value = 40), then a DNS query resulting in an authoritative HOST_NOT_FOUND response will be treated as a temporary error (a 450 error), rather than being rejected with a permanent rejection (a 550 error)  as    would otherwise normally cause.

New in 8.0, bit 6 (value = 64) modifies the effect of setting bit 3 (value = 8) on domain validity checks. With both these bits set, if the domain in the MAIL FROM address corresponds to a null MX domain, that address will be rejected as invalid. That is, setting bit 6 causes the bit 3 domain check to also implement support for.

Note that the   MTA option can be  used to set an MTA system default for this sort of behavior.

See also:
 * Notification messages
 * return_envelope MTA Option
 * mailfromdnsverify Option
 * Postmaster addresses
 * error_text_invalid_return_address MTA Option
 * error_text_unknown_return_address MTA Option
 * error_text_mailfromdnsverify MTA Option
 * error_text_null_mx MTA Option
 * Notification messages and postmaster messages channel options
 * Channel options