Beginning withV8.10, sendmail allows [IPC] delivery agents to also connect to Unix
domain sockets (?§20.5.2.4 on page 740). Some current versions of sendmail allow the
name [TCP] to be a synonym for [IPC], but [TCP] is deprecated as of V8.10, and
removed from V8.12, and should not be used. The $u sendmail macro should never be
included in the A= for this internal name.
P=[FILE]
Beginning withV8 sendmail, the internal name [FILE] specifies that delivery will be
made by appending the message to a file. This name is intended for use by the *file*
delivery agent (?§20.4.6 on page 725). [FILE] can be useful for designing a custom
delivery agent whose purpose is to append to files (perhaps coupled with the U=
delivery agent equate, ?§20.5.17 on page 755, to force particular ownership of the file).
P=[LPC]
The special internal name [LPC] (for local person communication) causes sendmail to
run in a sort of debugging mode. In this mode, you act as an SMTP server, interacting
with the sendmail program??™s standard input and output.
The [LPC] mode can be very helpful in tracking down mail problems. Consider the
mystery of duplicate five-character ???From ??? header lines that appear at the beginning of a
mail message when mail is sent with UUCP. To solve the mystery, make a copy of your
sendmail.cf file and in that copy change the P= for the UUCP delivery agent to [LPC]:
Muucp, P=/usr/bin/uux, F=msDFMhuU, S=13, R=23, A=uux - -r $h!rmail ($u)
?†“
change to
?†“
Muucp, P=[LPC], F=msDFMhuU, S=13, R=23, A=uux - -r $h!rmail ($u)
Then run sendmail by hand to see what it is sending to the uux program:
# /usr/lib/sendmail -Ccopy.
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