Exchange Database –> EDB and STM Files
2008-12-22 Initial Post
Exchange Server 2003
From knowledge gained in Microsoft Exchange Server 2003 Advanced Administration by J. McBee, May 2006.
Each information store (either mailbox of public) actually consists of two stores:
• The EDB file stores messages sent by MAPI clients (full Outlook client).
• The STM file contains messages sent by Internet clients (Outlook Express, OWA, IMAP) and is stored in native format (usually MIME).
Exchange will convert the message formats from one storage format to another on-the-fly based on the type of client and which store the message was in at the time. The messages and their attachments don’t get converted to the opposite format unless the opposite client modified the messages or attachments. The modified messages or attachments are then converted and saved to the saving client’s message store. NOTE: Modifying the message body doesn’t convert the attachment; the attachment is only converted when it’s actually modified. I tested this out by modifying an OWA message body and then its attachment in MAPI Outlook.
This makes sense and is worth noting: if you’re a hosted Exchange provider and most of your clients are non-MAPI, then your STM file will grow at a faster pace than your EDB file. The opposite would also be true; in a corporate environment with mostly Outlook MAPI users, the EDB file will grow at a faster pace than the STM file. I tested this out by attaching a 5 MB file from OWA and then attaching another 5 MB file from MAPI Outlook and saving both as drafts. The respective store file (EDB or STM) grew by at least 5 MB (the STM file actually grew by 8 MB, so EDB seems to store the attachments more efficiently).
