Notes about safe MDAs.

svn path=/trunk/; revision=3225

2 files changed, 22 insertions, 14 deletions

diff --git a/configure.in b/configure.in
index db7b899f..c1cbe481 100644
--- a/configure.in
+++ b/configure.in
@@ -212,6 +212,13 @@ AC_DEFINE_UNQUOTED(PID_DIR, "$dir")
 # it won't try delivering through local SMTP and cause a mail loop.
 # Sendmail without the -t option to use the message headers will work too,
 # not just for sendmail itself but for workalikes like exim.
+#
+# Note: it would be a very bad idea to use any MDA that doesn't return
+# a refuse-to-deliver status on disk- or process-table-full
+# conditions; mail could get lost that way.  Both procmail and
+# sendmail (and all of the MDAs like exim that might be lurking under
+# a sendmail alias) do the right thing in this circumstance.
+#
 AC_PATH_PROG(procmail, procmail, "", $PATH:/usr/sbin)
 if test "$procmail"
 then
diff --git a/fetchmail.man b/fetchmail.man
index 921fc754..f1856dda 100644
--- a/fetchmail.man
+++ b/fetchmail.man
@@ -350,20 +350,21 @@ be comma-separated.
 .B \-m <command>, \--mda <command>
 (Keyword: mda)
 You can force mail to be passed to an MDA directly (rather than
-forwarded to port 25) with the -mda or -m option.  Be aware that this
-disables some valuable resource-exhaustion checks and error handling
-provided by SMTP listeners; it's not a good idea unless running an
-SMTP listener is impossible.  If \fIfetchmail\fR is running as root,
-it sets its userid to that of the target user while delivering mail
-through an MDA.  Some possible MDAs are "/usr/sbin/sendmail -oem -f %F
-%T", "/usr/bin/deliver" and "/usr/bin/procmail -d %T" (but the latter
-is usually redundant as it's what SMTP listeners usually forward
-to).  Local delivery addresses will be inserted into the MDA command
-wherever you place a %T; the mail message's From address will be
-inserted where you place an %F.  Do \fInot\fR use an MDA invocation
-like "sendmail -oem -t" that dispatches on the contents of To/Cc/Bcc,
-it will create mail loops and bring the just wrath of many postmasters
-down upon your head.
+forwarded to port 25) with the -mda or -m option.  To avoid losing
+mail, use this option only with MDAs like procmail or sendmail that
+return a nonzero status on disk-full and other resource-exhaustion
+errors; the nonzero status tells fetchmail that delivery failed and
+prevents the message from being deleted off the server.  If
+\fIfetchmail\fR is running as root, it sets its userid to that of the
+target user while delivering mail through an MDA.  Some possible MDAs
+are "/usr/sbin/sendmail -oem -f %F %T", "/usr/bin/deliver" and
+"/usr/bin/procmail -d %T" (but the latter is usually redundant as it's
+what SMTP listeners usually forward to).  Local delivery addresses
+will be inserted into the MDA command wherever you place a %T; the
+mail message's From address will be inserted where you place an %F.
+Do \fInot\fR use an MDA invocation like "sendmail -oem -t" that
+dispatches on the contents of To/Cc/Bcc, it will create mail loops and
+bring the just wrath of many postmasters down upon your head.
 .TP 
 .B \--lmtp
 (Keyword: lmtp)