Aggregate e-mails when node belongs to more than one group

Problem/Motivation

When a node is added tot multiple groups, the notification is sent to all members of each group. When a member belongs to more than one group, he will receive duplicate e-mails.

Steps to reproduce

• Add an article
• Add the article to several groups with members belonging to multiple groups
• Check the number of e-mails received.

Proposed resolution

Send one e-mail per member of the grouped and deduplicated groups.

Remaining tasks

User interface changes

API changes

Data model changes