User restrictions can be made based on the user permission level (Approver, Designer, etc.,), i.e. if you set the Designer, the mail will be sent only to the designer from your selection group. The emails can be sent through desktop email client. It also has the ability to send emails among multiple groups. The Group Email web part is sure to fit the needs of the users who would like to send bulk email in their SharePoint farm. 1)Create and send bulk e-mail based on the group users e-mail address. 2)Supports only SharePoint Server 2010 and also SharePoint Online. 3)Select Custom site group as well as standard groups 4)Ability to send emails among multiple groups. 5)Permissions management (to restrict which users can send group emails)

• Email Web Part 1.6
  ArtfulBits Email Web Part allows sending e-mail messages directly from Microsoft SharePoint site. You can notify task assigned users, send gratitude or just send regular e-mail...

• Virto SharePoint Workflow Activities Kit 5.1.3
  SharePoint Workflow Activities Extensions Kit is a no-code set of SharePoint extensions for creating custom workflows using tools such as SharePoint Designer, Visual Studio and Visio