To avoid trouble as descbried in boo#1192916

---
 mailx.1 |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- mailx.1
+++ mailx.1	2021-11-23 12:33:48.788947209 +0000
@@ -4793,6 +4793,20 @@ mailaddr(7),
 sendmail(8)
 .SH NOTES
 .PP
+If used in systemd unit files not using
+.B Type=forking
+it is required to set the option
+.I sendwait
+on the command line of
+.BR mailx (1)
+with
+.I \-S sendwait=yes
+as otherwise it might happen that the
+.BR systemd (1)
+service manager will terminate the asynchronously
+started SMTP transfer as described at the option
+.IR smtp.
+.PP
 Variables in the environment passed to
 .I mailx
 cannot be unset.