I’ve been fighting K9Mail for weeks now, trying to get it to sync with MailStreet who hosts “exchange.ms”) hosted Exchange. If you’ve already followed the instructions at the K9Mail Wiki with no success, read on.

Thanks to the k9mail wiki on debugging connection issues and the fact that I already had the Android SDK installed, I was able to solve the 2 related errors I was getting. I would either get an “HTTP 404 not found” or an “HTTP 501 Not Implemented” depending on the settings I chose. With no additional settings other than suggested in the Wiki, I’d get a “501 not implemented”. If I tried to set a mailbox path, or a WebDAV path, I’d get the HTTP 404 Not Found.

In the debugging log, I saw that the system was calling “http://mail.$domain.exchange.ms/”$webDAVpath/Inbox – if I set it to a full URL, the full URL was getting appended. When I attempted to hit those same paths in a full browser, I’d always get an HTTP 404. So, digging in my history in Firefox, I found the following (cleaned) path:
In this case $emailaddress was my Exchange mail address with the “@” stripped out. Appending “Inbox” to the end of this path resulted in a valid load of my OWA inbox.

Plugging then: /exchange/$emailaddress/ into the WebDAV box in K9Mail, and my email immediately loaded up.

Now I have Android syncing my calendars and contacts, and k9mail is handling my massive inbox!