[exim] Problems with NDR messages to external recipients

Hi all!
I expirience strange Exim 4.68 error - it incorrectly sends NDR messages.

The problem is that Exim doesn't specify andy domain in HELO/EHLO while sending NDR to extenral users.
However, messages submitted by daemon (httpd forms and so on) are sent without any errors, as well as user-submitted messages are.

Receiving server answers:
rejected HELO from mydomain.com : syntactically invalid argument(s): (no argument given)

Debug on sending server shows the following:
22:06:32 30964 SMTP>> EHLO
22:06:32 30964 waiting for data on socket
22:06:32 30964 read response data: size=44
22:06:32 30964 SMTP<< 501 Syntactically invalid EHLO argument(s)
22:06:32 30964 SMTP>> HELO
22:06:32 30964 waiting for data on socket
22:06:32 30964 read response data: size=44
22:06:32 30964 SMTP<< 501 Syntactically invalid HELO argument(s)
22:06:32 30964 ok=0 send_quit=1 send_rset=1 continue_more=0 yield=0 first_address is not NULL
22:06:32 30964 SMTP>> QUIT

primary_hostname and qualify_domain are specified and point to mydomain.com
Also, the server's FQDN is mydomain.com.
Googling and duscussing this on forums was not successfull.
Anyone having any ideas?