mrep: Set From header according to To/Cc/Bcc header

If any of the address contained in the aforementioned headers matches an
address configured in the Reply-From header in mblaze-profile(5).

Without this change, mrep(1) uses the mail address configured as
Local-Mailbox for the From header. While generally desirable, I use
different mail addresses for different proposes. As such, I do not
want to reply to mails I received through my work address with my
private email address.

man/mblaze-profile.5

@@ -44,6 +44,9 @@ to recognize messages sent to you.
 A comma-separated list of mail addresses that also belong to you, for
 .Xr mscan 1
 to recognize messages sent by or directly to you.
+.It Li Reply-From\&:
+A comma-separated list of mail addresses that are automatically used for
+the From header in a reply if present in the Cc, To, or Bcc header.
 .It Li FQDN\&:
 The fully qualified domain name used for
 .Li Message\&-Id\&:

mcom

@@ -15,6 +15,11 @@ notmine() {
 	grep -Fv -e "$mine"
 }
 
+replyfrom() {
+	addrs="$(maddr -a -h reply-from: "$MBLAZE/profile")"
+	grep -F -e "$addrs"
+}
+
 ouniq() {
 	awk '!seen[$0]++'
 }
@@ -356,7 +361,15 @@ fi
 				msed "/body/d" /dev/stdin
 		fi | sed '/^$/d'
 		printf 'Subject: Re: %s\n' "$(COLUMNS=10000 mscan -f '%S' "$1")"
-		from=$(mhdr -h local-mailbox "$MBLAZE/profile")
+
+		addr=$(maddr -a -h to:cc:bcc: "$1" | replyfrom | head -n1)
+		if [ -n "$addr" ]; then
+			from=$(maddr -h reply-from "$MBLAZE/profile" | grep -Fi "<$addr>" | head -n1)
+		fi
+		if [ -z "$from" ]; then
+			from=$(mhdr -h local-mailbox "$MBLAZE/profile")
+		fi
+
 		[ "$from" ] && printf 'From: %s\n' "$from"
 		mid=$(mhdr -h message-id "$1")
 		if [ "$mid" ]; then