We just finished also the plugin part of our Exchange Integration. Over the last year we built a server side Exchange integration that synchronizes Contacts, Tasks and Calendar Items with the Exchange server from sever to server. No plugin is needed which eases the maintenance part and also the distributed logic. Over years we had experience with first the SugarCRM Plugin and then later also (less but still) with our own Outlook Plugin that took care of that synchronization.
Our server side Connectivity eases that and takes the component of too many outlook clients that end up all behaving slightly different depending on other components on windows installed.
To complete that we added now the plugin for email archiving and address book lookup when composing emails. As we see it those two steps need user interaction on the frontend and thus cannot be automated. A simple plugin allows to find related records in SpiceCRM and archive the email linked to those. In the same matter you can search contacts online directly out of Office365 or Outlook (for MAC and Windows) and use the information to find email addresses.
The Outlook Plugin we will make available as general part of SpiceCRM. The Exchange Integration is a commercial Plugin you can license from us.