Outlook Web Access
From MozillaZine Knowledge Base
OWA also supports accessing other users mailboxes if you're granted full access rights to the mailbox. If you need to do that DavMail might be your best bet. See this thread for how to deal with changes in OWA due to Exchange 2007.
Freepops is a add-on that supports many different webmail implementations. It looks like they've started a project to add support for OWA to FreePOPs. Take a look in thier forums to find the status.
MrPostman has two scripts to support OWA.
Pop2OWA Open source mail proxy program for Outlook Web Access. Versions 1.x (VB6) use WebDAV messages. Versions 2.x are re-writed in C# and use Exchange Web Services in order to support new Exchange 2007 & 2010 servers.
fetchExc is a program written in Java to fetch mail from OWA
The webmail extension author has posted instructions on how to configure a generic webmail extension for a domain and suggested it could be used to access a Microsoft Exchange server via HTTP. However, he also stated that the extension just responds to Thunderbird commands - you need to provide provide the login and download code.
DavMail is a POP/IMAP/SMTP/Caldav/CardDAV/LDAP gateway allowing any e-mail/calendar client to access Exchange via OWA. Its written in Java and doesn't seem to require tweaking any scripts like the other solutions do. CardDAV (it synchronizes contact data) can be used in Thunderbird with the SOGo Connector add-on. Using DavMail Gateway To Allow Thunderbird To Access Microsoft Exchange Server 2007 & Earlier has links to Thunderbird specific instructions.