FM

F=M

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Need Message-ID: in header

All versions

The F=M delivery agent flag is used by sendmail.cf header commands to force the inclusion of message identification information (F=):

 H?M?Re-sent-Message-ID: <$t.$i@$j> H?M?Message-ID: <$t.$i@$j> 

The F=M delivery agent flag has no special internal meaning to sendmail . It is a convention that is used only in the assorted Message-ID : header definitions (Message-ID:). See F= for a general description of this process.

Note that the Message-ID : header definition should always be included in the sendmail.cf file because many software packages expect the presence of that header.