- Connect to outlook feature is available only to these type of lists: Calendar, Tasks, Project Tasks, Contacts, Document Library and Discussion Boards.
- Prior to Service pack 1: If your SharePoint site has Minimal Download Strategy feature enabled, simply press "F5" to reload the current page. You'll get connect to outlook button enabled! Disabling MDS feature is not a good idea IMHO!!
- Make sure that "SharePoint Stssync Handler" is enabled in browser add-ons. (IE >> Tools >> Manage Add-ons)
- Check the client-integration option of web application settings
- This feature works only when you have 32 bit version of office installed in your client machine!
- The "WebClient" Service must be running in services console of the client machine!
- Try adding your SharePoint site to "Trusted sites zone", Also uncheck "Enhanced Protected Mode" for the zone.
- Logged user must have at least "Read" permissions to SharePoint . "View Only" doesn't work!
I was trying it with custom list & the feature itself is not available
I found that this is not possible. If you need to sync a todo list, create a task list. Then you can delete all the columns that don't interest you, and add whatever columns you want to use.
The same goes for calendar, if you want a list syncronised with your outlook calendar, then create a calendar list and customize it to your needs.