--- smtpd/mda.c.orig 2016-05-13 02:56:04.000000000 +1000 +++ smtpd/mda.c 2018-04-26 10:28:45.373358000 +1000 @@ -274,7 +274,7 @@ * if any */ n = iobuf_fqueue(&s->iobuf, - "Return-Path: %s\n" + "Return-Path: <%s>\n" "Delivered-To: %s\n", e->sender, e->rcpt ? e->rcpt : e->dest);