10.10.4.5 To Send, Block and Specify Status Notification Messages to the Postmaster
By default, a copy of failure and warning status notification messages are sent to the postmaster unless error returns and warnings are completely suppressed with a blank Errors-to: header line or a blank envelope From: address. Further granularity of notification message delivery to the postmaster can be controlled by a number of channel keywords described in the sections below and in Table 10–12. This section consists of the following subsections:
Returned Failed Messages
Keywords: sendpost, nosendpost, copysendpost, errsendpost
A channel program may be unable to deliver a message because of long-term service failures or invalid addresses. When this occurs, the MTA channel program returns the message to the sender with an accompanying explanation of why the message was not delivered. Optionally, a copy of all failed messages is sent to the local postmaster. This is useful for monitoring message failures, but it can result in an excessive amount of traffic with which the postmaster must deal. (See Table 10–12.)
Warning Messages
Keywords:warnpost, nowarnpost, copywarnpost, errwarnpost
In addition to returning messages, the MTA can send detailed warnings for undelivered messages. This is generally due to time-outs based on the setting of the notices channel keyword, although in some cases channel programs may produce warning messages after failed delivery attempts. The warning messages contain a description of what’s wrong and how long delivery attempts continue. In most cases they also contain the headers and the first few lines of the message in question.
Optionally, a copy of all warning messages can be sent to the local postmaster. This can be somewhat useful for monitoring the state of the various queues, although it does result in lots of traffic for the postmaster to deal with. The keywords warnpost, copywarnpost, errwarnpost, and nowarnpost are used to control the sending of warning messages to the postmaster. (See Table 10–12.)
Blank Envelope Return Addresses
The returnenvelope keyword takes a single integer value, which is interpreted as a set of bit flags. 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 address.
Note –
The use of a blank address is mandated by RFC 1123. However, some systems do not properly handle blank envelope From: addresses 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. This is used to accommodate noncompliant systems that do not conform to RFC 821, RFC 822, or RFC 1123.
Bit 2 (value = 4) prohibits syntactically invalid return addresses.
Bit 3 (value = 8) same as mailfromdnsverify keyword.
Postmaster Returned Message Content
Keywords:postheadonly, postheadbody
When a channel program or the periodic message return job returns messages to both the postmaster and the original sender, the postmaster copy can either be the entire message or just the headers. Restricting the postmaster copy to just the headers adds an additional level of privacy to user mail. However, this by itself does not guarantee message security; postmasters and system managers are typically in a position where the contents of messages can be read using root system privileges, if they so choose. (See Table 10–12.)
Setting Per Channel Postmaster Addresses
Keywords: aliaspostmaster, returnaddress, noreturnaddress, returnpersonal, noreturnpersonal
By default, the Postmaster’s return address that is used when the MTA constructs bounce or status notification messages is postmaster@local-host, where local-host is the official local host name (the name on the local channel), and the Postmaster personal name is “MTA e-Mail Interconnect.” Care should be taken in the selection of the Postmaster address—an illegal selection may cause rapid message looping and a great number of error messages.
The RETURN_ADDRESS and RETURN_PERSONAL options can be used to set an MTA system default for the Postmaster address and personal name. Or, if per channel controls are desired, the returnaddress and returnpersonal channel keywords may be used. returnaddress and returnpersonal each take a required argument specifying the Postmaster address and Postmaster personal name, respectively. noreturnaddress and noreturnpersonal are the defaults and signify that the default values should be used. The defaults are established via the RETURN_ADDRESS and RETURN_PERSONAL options or the normal default values if such options are not set.
If the aliaspostmaster keyword is placed on a channel, then any messages addressed to the user name postmaster (lowercase, uppercase, or mixed case) at the official channel name is redirected to postmaster@local-host, where local-host is the official local host name (the name on the local channel). Note that Internet standards require that any domain in the DNS that accepts mail have a valid postmaster account that receives mail. So this keyword can be useful when it is desired to centralize postmaster responsibilities, rather than setting separate postmaster accounts for separate domains. That is, whereas returnaddress controls what return postmaster address is used when the MTA generates a notification message from the postmaster, aliaspostmaster affects what the MTA does with messages addressed to the postmaster.
Table 10–12 Keywords for Sending Notification Messages to the Postmaster and Sender
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