diff --git a/Documentation/config/sendemail.txt b/Documentation/config/sendemail.txt
index 51da7088a8..92a9ebe98c 100644
--- a/Documentation/config/sendemail.txt
+++ b/Documentation/config/sendemail.txt
@@ -61,6 +61,7 @@ sendemail.ccCmd::
 sendemail.chainReplyTo::
 sendemail.envelopeSender::
 sendemail.from::
+sendemail.headerCmd::
 sendemail.signedoffbycc::
 sendemail.smtpPass::
 sendemail.suppresscc::
diff --git a/Documentation/git-send-email.txt b/Documentation/git-send-email.txt
index b0f438ec99..295a3dd67c 100644
--- a/Documentation/git-send-email.txt
+++ b/Documentation/git-send-email.txt
@@ -320,6 +320,14 @@ Automating
 	Output of this command must be single email address per line.
 	Default is the value of `sendemail.ccCmd` configuration value.
 
+--header-cmd=<command>::
+	Specify a command that is executed once per outgoing message
+	and output RFC 2822 style header lines to be inserted into
+	them. When the `sendemail.headerCmd` configuration variable is
+	set, its value is always used. When --header-cmd is provided
+	at the command line, its value takes precedence over the
+	`sendemail.headerCmd` configuration variable.
+
 --[no-]chain-reply-to::
 	If this is set, each email will be sent as a reply to the previous
 	email sent.  If disabled with "--no-chain-reply-to", all emails after
diff --git a/git-send-email.perl b/git-send-email.perl
index b8d77ad214..906fc1964d 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -88,8 +88,9 @@ sub usage {
 
   Automating:
     --identity              <str>  * Use the sendemail.<id> options.
-    --to-cmd                <str>  * Email To: via `<str> \$patch_path`
-    --cc-cmd                <str>  * Email Cc: via `<str> \$patch_path`
+    --to-cmd                <str>  * Email To: via `<str> \$patch_path`.
+    --cc-cmd                <str>  * Email Cc: via `<str> \$patch_path`.
+    --header-cmd            <str>  * Add headers via `<str> \$patch_path`.
     --suppress-cc           <str>  * author, self, sob, cc, cccmd, body, bodycc, misc-by, all.
     --[no-]cc-cover                * Email Cc: addresses in the cover letter.
     --[no-]to-cover                * Email To: addresses in the cover letter.
@@ -270,7 +271,7 @@ sub do_edit {
 # Variables with corresponding config settings
 my ($suppress_from, $signed_off_by_cc);
 my ($cover_cc, $cover_to);
-my ($to_cmd, $cc_cmd);
+my ($to_cmd, $cc_cmd, $header_cmd);
 my ($smtp_server, $smtp_server_port, @smtp_server_options);
 my ($smtp_authuser, $smtp_encryption, $smtp_ssl_cert_path);
 my ($batch_size, $relogin_delay);
@@ -319,6 +320,7 @@ sub do_edit {
     "tocmd" => \$to_cmd,
     "cc" => \@config_cc,
     "cccmd" => \$cc_cmd,
+    "headercmd" => \$header_cmd,
     "aliasfiletype" => \$aliasfiletype,
     "bcc" => \@config_bcc,
     "suppresscc" => \@suppress_cc,
@@ -520,6 +522,7 @@ sub config_regexp {
 		    "compose" => \$compose,
 		    "quiet" => \$quiet,
 		    "cc-cmd=s" => \$cc_cmd,
+		    "header-cmd=s" => \$header_cmd,
 		    "suppress-from!" => \$suppress_from,
 		    "no-suppress-from" => sub {$suppress_from = 0},
 		    "suppress-cc=s" => \@suppress_cc,
@@ -1766,17 +1769,15 @@ sub process_file {
 	$subject = $initial_subject;
 	$message = "";
 	$message_num++;
-	# First unfold multiline header fields
+	# Retrieve and fold header fields.
+	my @header_lines = ();
 	while(<$fh>) {
 		last if /^\s*$/;
-		if (/^\s+\S/ and @header) {
-			chomp($header[$#header]);
-			s/^\s+/ /;
-			$header[$#header] .= $_;
-	    } else {
-			push(@header, $_);
-		}
+		push(@header_lines, $_);
 	}
+	@header = fold_headers(@header_lines);
+	# Add computed headers, if applicable.
+	push @header, invoke_header_cmd($header_cmd, $t) if defined $header_cmd;
 	# Now parse the header
 	foreach(@header) {
 		if (/^From /) {
@@ -2022,6 +2023,32 @@ sub execute_cmd {
 	return @lines;
 }
 
+# Process headers lines, folding multiline headers as defined by RFC
+# 2822.
+sub fold_headers {
+	my @headers;
+	foreach(@_) {
+		last if /^\s*$/;
+		if (/^\s+\S/ and @headers) {
+			chomp($headers[$#headers]);
+			s/^\s+/ /;
+			$headers[$#headers] .= $_;
+		} else {
+			push(@headers, $_);
+		}
+	}
+	return @headers;
+}
+
+# Invoke the provided CMD with FILE as an argument, which should
+# output RFC 2822 email headers. Fold multiline headers and return the
+# headers as an array.
+sub invoke_header_cmd {
+	my ($cmd, $file) = @_;
+	my @lines = execute_cmd("header-cmd", $header_cmd, $file);
+	return fold_headers(@lines);
+}
+
 # Execute a command (e.g. $to_cmd) to get a list of email addresses
 # and return a results array
 sub recipients_cmd {
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 0de83b5d2b..3393725107 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -374,13 +374,16 @@ test_expect_success $PREREQ,!AUTOIDENT 'broken implicit ident aborts send-email'
 	)
 '
 
-test_expect_success $PREREQ 'setup tocmd and cccmd scripts' '
+test_expect_success $PREREQ 'setup cmd scripts' '
 	write_script tocmd-sed <<-\EOF &&
 	sed -n -e "s/^tocmd--//p" "$1"
 	EOF
-	write_script cccmd-sed <<-\EOF
+	write_script cccmd-sed <<-\EOF &&
 	sed -n -e "s/^cccmd--//p" "$1"
 	EOF
+	write_script headercmd-sed <<-\EOF
+	sed -n -e "s/^headercmd--//p" "$1"
+	EOF
 '
 
 test_expect_success $PREREQ 'tocmd works' '
@@ -410,6 +413,20 @@ test_expect_success $PREREQ 'cccmd works' '
 	grep "^	cccmd@example.com" msgtxt1
 '
 
+test_expect_success $PREREQ 'headercmd works' '
+	clean_fake_sendmail &&
+	cp $patches headercmd.patch &&
+	echo "headercmd--X-Debbugs-CC: dummy@example.com" >>headercmd.patch &&
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--header-cmd=./headercmd-sed \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		headercmd.patch \
+		&&
+	grep "^X-Debbugs-CC: dummy@example.com" msgtxt1
+'
+
 test_expect_success $PREREQ 'reject long lines' '
 	z8=zzzzzzzz &&
 	z64=$z8$z8$z8$z8$z8$z8$z8$z8 &&
