Error sending Mails to Distribution List

Hello,

I just figured out a very serious problem! It seems Askozia cannot send mails to a exchange distribution list. Due to the fact that it is not possible to enter several recipients I created a distribution list on our server and used it on askozia for fax recipients.

Here is what the Askozia log says:

Sep 1 16:37:02 msmtp: host=xxxx.xxxx.xxxx tls=off auth=off from=xxxx@xxx.xx recipients=xxxx@xxx.xx smtpstatus=550 smtpmsg='550 5.1.1 User unknown' errormsg='recipient address xxx@xxx.xx not accepted by the server' exitcode=EX_

I Double checked my distribution list and and I can send mails from my outlook to it without any problems.

Here is a part of the log of our mailserver:

,*,SMTPSubmit SMTPAcceptAnySender SMTPAcceptAuthoritativeDomainSender AcceptRoutingHeaders,Set Session Permissions
>,"220 xxxx.xxxx.xxxx Microsoft ESMTP MAIL Service ready at Thu, 1 Sep 2011 16:36:56 +0200",
<,EHLO localhost,
>,250-xxxx.xxxx.xxxx Hello [xxx.xxx.xxx.xxx],
>,250-SIZE,
>,250-PIPELINING,
,>,250-DSN,
,>,250-ENHANCEDSTATUSCODES,
>,250-STARTTLS,
>,250-X-ANONYMOUSTLS,
>,250-AUTH NTLM,
>,250-X-EXPS GSSAPI NTLM,
>,250-8BITMIME,
>,250-BINARYMIME,
>,250-CHUNKING,
>,250-XEXCH50,
>,250-XRDST,
>,250 XSHADOW,
<,MAIL FROM:<xxxx@xxx.xx>,
*,08CE19171ABD41F2;2011-09-01T14:36:56.817Z;1,receiving message
>,250 2.1.0 Sender OK,
<,RCPT TO:<xxx@xxx.xx>,
*,Tarpit for '0.00:00:05',
>,550 5.1.1 User unknown,
<,DATA,
*,Tarpit for '0.00:00:05',
>,503 5.5.2 Need rcpt command,
-,,Remote

So it seems for distribution lists the usage of the RCPT TO command is not allowed. Or do I need to change something on our mailserver?

Greetings, Max.