Outlook add-in for Office 365:
The Insightly Sidebar for Outlook is available to customers using Outlook with their own Office 365 business plan subscription plan. With the add-in, you can view and add Insightly records right from your inbox.
All Outlook versions:
For those of you with other versions of Outlook or no direct subscription to Office 365, you can still forward or CC messages from Outlook to save them to Insightly. You can also use this method if you don't want to install the add-in.
Insightly does not support NTLM or GSSAPI authentication methods. If you use either of these, Insightly may be blocked from connecting to your server.
Customers on paid Insightly plans who use Microsoft Exchange with Outlook can sync Insightly with their Outlook calendars.
If you have a free Insightly account, you can view your Insightly calendar in Outlook by adding the Insightly calendar feed.
You can export contacts from Outlook and import them into Insightly. Insightly does not offer a contact sync for Outlook.
If you are interested in contact sync, you can also look into a fee-based service like PieSync. They are not affiliated with Insightly, but offer an option to sync to and from Insightly.