Undeliverable mail, invalid header section

The message WAS NOT relayed to:
<shop@mydomain.net>:
554 5.6.0 bounce, id=61451-01 - bad header

This nondelivery report was generated by the program amavisd-new at host
srv.mydomain.net. Our internal reference code for your message is
61451-01/rBDG0yUfB-Sm

INVALID HEADER

Missing required header field: "Date"

Return-Path: <noreply@xxxx.eu>
From: "mypos.eu" <noreply@xxxxs.eu>
X-Mailer: iMailGate
Subject: xxxxx e-mail


Can anyone help me?

It looks like this modification in AMAVIS config solved the problem in my case:
# Selectively disable some of the header checks
#
# Duplicate or multiple occurrence of a header field
$allowed_header_tests{'multiple'} = 0;

# Missing some headers. e.g. 'Date:'
$allowed_header_tests{'missing'} = 0;

Found the answer here: https://forum.iredmail.org/topic10400-iredadminpro-support-error-554-560-with-bad-header.html