Q:

Outlook/SharePoint calendar sync 'error occurred connecting to site'

Our SharePoint site was originally setup under a test name (oldname). When brought into production, I added an AAM to extend it to our production name (prodname). About 6 months ago, I added an SSL redirect in IIS which sends all http requests to https. With the addition of the SSL redirect, Outlook/SharePoint calendar syncing stopped working.
In Outlook, users are getting the error 'Task 'SharePoint' reported error (0x0004010F).  'The SharePoint List (Develop - Calendar) cannot be found  If the problem continues, contact the SharePoint site admin.  HTTP 404.  An error occurred connecting to http://oldname.com/sites/abc/develop.  A connection to http://prodname.com/sites/abc/develop, an alternate Web address for this SharePoint site, will be attempted'
Task 'SharePoint' reported error (0x80070005):  'You do not have permission to view this SharePoint List (Develop - Calendar).  Contact the SharePoint site administrator.  HTTP 303.'
My AAMs look like this for mapping collection: 'oldname.com'
Internal URL      ------         Zone     --------   Public URL for Zone
http://oldname.com  Default         http://oldname.com
http://prodname.com Internet                 http://prodname.com
https://prodname.com    Custom          https://prodname.com
I think I should also have the entry:
http://prodname.com Custom          https://prodname.com
but according to what I've read, I can't have duplicate Internal URLs for the collection yet I also must have an entry where the Internal and Public URLs match.  
Or perhaps it's not an AAM issue?  Any advice would be greatly appreciated!  Thanks. 

A:

You just have to set up the calendar sync with the appropriate web address using HTTPS. The error is telling you it's trying to connect to http://oldname.com/sites/abc/develop which isn't the URL you want configured. As a fallback, it is attempting to pull the calendar from http://prodname.com/sites/abc/develop, but that's hitting your HTTP Redirect in IIS.
Configure the calendar overlay using https://prodname.com/sites/abc/develop and this issue should be resolved.
Also, make sure that all user accounts requesting the calendar have proper permissions on the calendar list.

