invalid header: missing required header field

[Voytek]

I send a similar email once or twice a week, normally, don't have any
issues, today, got a "Delivery status notification, invalid header
section: missing required header field" from my own server/amavisd:

so, in the amavisd warning message, 'from' is blank, in header in sent
folder, from is 'normal', has my name/email

was it just a 'glitch' ?
or what went wrong ? have I screwed up my amavisd setup ?

I've been using K9 mail client for ages, never struck such issue
----------------------
"Delivery status notification, invalid header section: missing required
header field
From:	"Content-filter at geko.sbt.net.au" <postmaster at geko.sbt.net.au>

Your message WAS SUCCESSFULLY RELAYED to:
  <someone at tld.au>
This delivery report was generated by the program amavisd-new at host
geko.sbt.net.au. Our internal reference code for your message is
22738-05/Tw8RKTuHo9Kk

INVALID HEADER: MISSING REQUIRED HEADER FIELD
  Missing required header field: "From"
Return-Path: <voytek at sbt.net.au>
From:
User-Agent: K-9 Mail for Android
Subject: xyz

MISSING REQUIRED HEADER FIELD

  The RFC 5322 document specifies rules for forming internet messages.
  Section '3.6. Field Definitions' specifies that certain header fields
  are required (origination date field and the "From:" originator field). "
-----------------

looking at my sent mail header, it shows:
-----------------
Date: Sat, 10 Feb 2018 15:30:03 +1100
From: Voytek <voytek at sbt.net.au>
To: aaaaaa
Subject: xyz
User-Agent: K-9 Mail for Android
Message-ID: <5E1A453C-93DB-4147-95E9-B423F1CF5226 at sbt.net.au>
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="----J99IMONX16ZRDCJD272V08X0LFLC15"
Content-Transfer-Encoding: 7bit
-----------------
from 'bounce' message:
----------------
Return-Path: <voytek at sbt.net.au>
Received: from nexus7 (110-175-246-167.tpgi.com.au [110.175.246.167])
        by geko.sbt.net.au (Postfix) with ESMTPSA id 1EED86667133
        for <someone at tld.au>; Sat, 10 Feb 2018 15:30:07 +1100
(AEDT)
Date: Sat, 10 Feb 2018 15:30:03 +1100
User-Agent: K-9 Mail for Android
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="----J99IMONX16ZRDCJD272V08X0LFLC15"
Content-Transfer-Encoding: 7bit