OS X 10.9.2 is out today. As usual, the newest Mail version (v7.2) rejects the DEVONthink Pro Office mail plugin. Quit Mail, launch DEVONthink, open Install Add Ons…, install the Mail plugin again, and all will be well.
DEVONthink automatically prompted me to reinstall the plugin this time-I believe that was a change with either the 2.7.2 or 2.7.3 release. I gather the auto-prompt didn’t happen for you?
No, the auto prompt never worked for me, this time or previously.