Email filtering can prevent the delivery of the invitation email to the Sales Insight Outlook Plug-in, preventing end users from being able to activate the plug-in.
This can be re-mediated by white-listing the trusted IP range from the following document:
The email invitation return path is determined by the Marketo user who is inviting in the instance. So if there is a restriction on the domain that the email can be sent from you can adjust this by creating a dummy user with a username with the a domain that would qualify for IT restrictions. Then log in as the dummy user and send the invitation. It will have the dummy address in the From line.
Who This Solution Applies To
Outlook Plug-In users