sendmail, 4th Edition

Macro-Included Headers Don’t Survive Queueing

The inclusion of a header based on a macro’s value is guaranteed to work only when mail is first sent or delivered, and can fail if the message is queued. Consider, for example, the desire to include a header that prints one of the sendmail program’s macro values:

LOCAL_CONFIG
H?${dsn_envid}?X-ENVID: ${dsn_envid}

The intention here is to record the value of the DSN envelope identifier value in an X- header, if such an identifier was supplied during the SMTP transaction. If a message is received with a MAIL From: line such as the following, the envelope identifier and ${dsn_envid} macro’s value will be given the text following the ENVID= expression:

MAIL From: <[e-mail]> ENVID=1234abcd5678

When this message is received, the ${dsn_envid} macro will contain a value (the string 1234abcd5678) which will cause the X-ENVID: header to be given a value:

X-ENVID: 1234abcd5678

If this message cannot be delivered right away and is deferred to the queue instead, the previous header will be stored in the queue like this:

H?${dsn_envid}?X-ENVID: 1234abcd5678

Note that the original mc file’s ?${dsn_envid}? test is included in the queue file. When this message is later delivered, the ${dsn_envid} macro will not have a value. That macro is given a value only when the message is first received with SMTP. As a consequence, when the message is delivered from the queue, the ${dsn_envid} macro will lack a value and thus the X-ENVID: header will not be included ...