Here you can find the solution to this error in MDaemon mail server. It's a post from Jay Tolbert at lists.altn.com:
Go to Setup -> Default Domain & Servers, Servers, uncheck ...refuses
messages which are not RFC compliant. That will allow MDaemon to accept
the malformed messages.
To be RFC compliant a message requires a Date header, which you will get
if missing with the other switch you checked, and either a single From
or Sender header (see help for full requirements). If you want to make
sure messages have a From header, you can do it with a content filter
rule. Go to Security -> Content Filter, New Rule. Name it something
like 'Add missing From header'. Check 'If the FROM HEADER contains' on
the left. Click on 'contains specific strings' at the bottom, click on
'contains', change 'contains' to 'Does Not Exist', click OK, click OK.
On the right click 'ADD an extra HEADER 1 to message'. At the bottom
click on 'specify information'. Put in 'From' as the header name and
$Header:X-Envelope-From$ as the header value. Click OK. Click OK to
save the rule. The X-Envelope-From header is the from address given
during the SMTP transaction. Generally, it will match the From header
inside the message though there are several situations, like list
messages, where it may be different.
