exim -DOPT=From:From -odf b@test.ex
From: nobody@example.com
+content
+****
+#
+# no header, multi-sign
+exim -DOPT=From:=X-Mine -odf b10@test.ex
+From: nobody@example.com
+
+content
+****
+#
+# double header, multi-sign
+exim -DOPT=From:=X-Mine -odf b12@test.ex
+From: nobody@example.com
+X-mine: one
+X-mine: two
+
+content
+****
+#
+#
+# no header, always-oversign
+exim -DOPT=+X-Mine -odf b20@test.ex
+From: nobody@example.com
+
+content
+****
+#
+# double header, always-oversign
+exim -DOPT=+X-Mine -odf b22@test.ex
+From: nobody@example.com
+X-mine: one
+X-mine: two
+
content
****
#