Spent a long time troubleshooting this issue with being unable to get Mail.app on Mavericks to sync an Exchange 2010 mailbox, I had tried a lot of steps in this thread already including removing the V2 folder from /Library/Mail and recreating accounts and such like but nothing worked.
What fixed it for me:
Open Mail.app>Preferences>Accounts
Highlight your Exchange account. Under the Account Information tab untick "Use Autodiscover Service"
Internal server address: use your OWA FQDN address such as mail.companyname.com
External server address: leave this blank
Click Advanced tab. Under the "External Server Path" - untick "Use SSL" so the external port defaults to 80
Leave the external and internal EWS paths as default on /EWS/Exchange.asmx
Click the General button at the top, and save changes
Do Mailbox>Get New Email
At that point all mail was sync'd at expected speed including subfolders etc
Hope that helps others.
Cheers