Curious if you've found any resolution since you posted this.  We are scheduled to be migrated 12/1 and have the same issue with thousands of proof users.  Unfortunately our proof users are contributors and not external users so that poses a greater chance of this notification going out.

We have been experiencing the same situation, I've had to be on 2 calls recently over one issue.  On another ticket, the suggestions that they made didn't make any sense for the problem that we were having.

@hkadkins and @yvanukuri03 can you give some examples of how you used your tasks for naming convention you mentioned on the calls and also your typical folder setup?

Hi Crystal are you looking for customized, because their is a system generated notification setting under requests I have made. 

One other area to look at might be to see if they have access to user contact information.  It is a default for admins but a check box on other levels.

Does the user have manage access to the report they're trying to send or just view access?  They also need edit access to  Edit access to Reports, Dashboards, Calendars and Edit access to Filters, Views, Groupings.