diff -Naur sendmail-8.12.11.original/include/libmilter/mfapi.h sendmail-8.12.11/include/libmilter/mfapi.h
--- sendmail-8.12.11.original/include/libmilter/mfapi.h	Tue Oct 21 07:51:49 2003
+++ sendmail-8.12.11/include/libmilter/mfapi.h	Thu Feb 19 16:21:23 2004
@@ -135,6 +135,9 @@
 #if _FFR_QUARANTINE
 # define SMFIF_QUARANTINE 0x00000020L	/* filter may quarantine envelope */
 #endif /* _FFR_QUARANTINE */
+#if _FFR_SETSENDER
+#define SMFIF_SETSENDER	0x00000040L	/* filter may set sender */
+#endif /* _FFR_SETSENDER */
 
 /*
 **  Continue processing message/connection.
@@ -367,6 +370,17 @@
 
 LIBMILTER_API int smfi_addrcpt __P((SMFICTX *, char *));
 
+#if _FFR_SETSENDER
+/*
+**  Set the sender address for the message
+**
+**	SMFICTX *ctx; Opaque context structure
+**	char *sender; Sender address to be set
+*/
+
+LIBMILTER_API int smfi_setsender __P((SMFICTX *, char *));
+
+#endif /* _FFR_SETSENDER */
 /*
 **  Add a recipient to the envelope
 **
diff -Naur sendmail-8.12.11.original/include/libmilter/mfdef.h sendmail-8.12.11/include/libmilter/mfdef.h
--- sendmail-8.12.11.original/include/libmilter/mfdef.h	Tue Nov 12 10:22:28 2002
+++ sendmail-8.12.11/include/libmilter/mfdef.h	Thu Feb 19 16:21:23 2004
@@ -24,11 +24,15 @@
 
 /* These apply to SMFIF_* flags */
 #define SMFI_V1_ACTS	0x0000000FL	/* The actions of V1 filter */
+#if _FFR_SETSENDER
+# define SMFI_V2_ACTS   0x0000007FL     /* The actions of V2 filter */
+#else
 #if _FFR_QUARANTINE
 # define SMFI_V2_ACTS	0x0000003FL	/* The actions of V2 filter */
 #else /* _FFR_QUARANTINE */
 # define SMFI_V2_ACTS	0x0000001FL	/* The actions of V2 filter */
 #endif /* _FFR_QUARANTINE */
+#endif /* _FFR_SETSENDER */
 #define SMFI_CURR_ACTS	SMFI_V2_ACTS	/* The current version */
 
 /* address families */
@@ -52,6 +56,9 @@
 # define SMFIC_RCPT		'R'	/* RCPT to */
 
 /* actions (replies) */
+#if _FFR_SETSENDER
+# define SMFIR_SETSENDER        's'     /* set sender */
+#endif /* _FFR_SETSENDER */
 # define SMFIR_ADDRCPT		'+'	/* add recipient */
 # define SMFIR_DELRCPT		'-'	/* remove recipient */
 # define SMFIR_ACCEPT		'a'	/* accept */
diff -Naur sendmail-8.12.11.original/libmilter/smfi.c sendmail-8.12.11/libmilter/smfi.c
--- sendmail-8.12.11.original/libmilter/smfi.c	Wed May  1 08:22:02 2002
+++ sendmail-8.12.11/libmilter/smfi.c	Thu Feb 19 16:21:23 2004
@@ -112,6 +112,37 @@
 	return r;
 }
 
+#if _FFR_SETSENDER
+/*
+**  SMFI_SETSENDER -- Set the sender address for the message
+**
+**	Parameters:
+**		ctx -- Opaque context structure
+**		rcpt -- recipient address
+**
+**	Returns:
+**		MI_SUCCESS/MI_FAILURE
+*/
+
+int
+smfi_setsender(ctx, sender)
+	SMFICTX *ctx;
+	char *sender;
+{
+	size_t len;
+	struct timeval timeout;
+
+	if (sender == NULL || *sender == '\0')
+		return MI_FAILURE;
+	if (!mi_sendok(ctx, SMFIF_SETSENDER))
+		return MI_FAILURE;
+	timeout.tv_sec = ctx->ctx_timeout;
+	timeout.tv_usec = 0;
+	len = strlen(sender) + 1;
+	return mi_wr_cmd(ctx->ctx_sd, &timeout, SMFIR_SETSENDER, sender, len);
+}
+
+#endif /* _FFR_SETSENDER */
 /*
 **  SMFI_ADDRCPT -- send an additional recipient to the MTA
 **
diff -Naur sendmail-8.12.11.original/sendmail/milter.c sendmail-8.12.11/sendmail/milter.c
--- sendmail-8.12.11.original/sendmail/milter.c	Tue Dec  2 10:57:44 2003
+++ sendmail-8.12.11/sendmail/milter.c	Thu Feb 19 16:21:23 2004
@@ -2803,6 +2803,55 @@
 		e->e_msgsize += strlen(h->h_value);
 	}
 }
+#if _FFR_SETSENDER
+/*
+**  MILTER_SETSENDER -- Set the sender address for the message
+**
+**	Parameters:
+**		response -- encoded form of recipient address.
+**		rlen -- length of response.
+**		e -- current envelope.
+**
+**	Returns:
+**		none
+*/
+
+static void
+milter_setsender(response, rlen, e)
+	char *response;
+	ssize_t rlen;
+	ENVELOPE *e;
+{
+	int olderrors;
+
+	if (tTd(64, 10))
+		sm_dprintf("milter_setsender: ");
+
+	/* sanity checks */
+	if (response == NULL)
+	{
+		if (tTd(64, 10))
+			sm_dprintf("NULL response\n");
+		return;
+	}
+
+	if (*response == '\0' ||
+	    strlen(response) + 1 != (size_t) rlen)
+	{
+		if (tTd(64, 10))
+			sm_dprintf("didn't follow protocol (total len %d != rlen %d)\n",
+				   (int) strlen(response), (int) (rlen - 1));
+		return;
+	}
+
+	if (tTd(64, 10))
+		sm_dprintf("%s\n", response);
+	olderrors = Errors;
+  	(void) setsender(response, e, NULL, '\0', false);
+ 	Errors = olderrors;
+	return;
+}
+#endif /* _FFR_SETSENDER */
 /*
 **  MILTER_ADDRCPT -- Add the supplied recipient to the message
 **
@@ -3739,6 +3788,19 @@
 				}
 				milter_changeheader(response, rlen, e);
 				break;
+
+#if _FFR_SETSENDER
+			  case SMFIR_SETSENDER:
+				if (!bitset(SMFIF_SETSENDER, m->mf_fflags))
+				{
+					if (MilterLogLevel > 9)
+						sm_syslog(LOG_WARNING, e->e_id,
+							  "milter_data(%s) lied about setting sender, honoring request anyway",
+							  m->mf_name);
+				}
+				milter_setsender(response, rlen, e);
+				break;
+#endif /* _FFR_SETSENDER */
 
 			  case SMFIR_ADDRCPT:
 				if (!bitset(SMFIF_ADDRCPT, m->mf_fflags))