When you generate documents and attach it to an email in a workflow it is oftenn ecessary to send emails with different senders.
This requires specific privilgeges in Microsoft Dynamics 365 CE otherwise you will get the following errormessage:
User does not have send-as privilege.
at AutoMergeService.MergeService.sendEmail(IOrganizationService iservice, Entity queueItem)
at AutoMergeService.MergeService.ProcessDocuments(MergeService parent, Int32& pendingRecords)
The necessary privilege here is a personal setting, called "Allow other Microsoft Dynamics 365 users to send email on your behalf".
If you need to set this setting for all or some of your users the easiest way is to use the one of the tools of the XRMToolBox. ( http://www.xrmtoolbox.com)
The tool called "User Settings Utility" gives you the possibility to set the setting ("Allow emails on my behalf") for multiple or all users in your organization.