From search results I send a message to a certain email address as attachment in the MS Outlook (.msg) format but the message is received as attachment in the Outlook Express (.eml) format. Why?

Support to Microsoft Exchange Server MAPI Client and Collaboration Data Objects  might not be installed on the Archive Server for MDaemon machine. Typically, this package is not installed on a system on which any version of Microsoft Outlook or Microsoft Exchange Server 2003 or earlier is installed.

MAPI support required by this Archive Server for MDaemon feature may be downloaded from here.

Note: After installation of MAPI support please, restart the server for changes to take effect.