SharePoint 2013: users not receiving email notifications from workflows

Problem

Users complain that they are not receiving email notifications from various workflows, such as ticketing workflows.  You test email alerts and find that you receive them successfully.  You ask other users, and you find that they are also receiving email notifications.  A few other users have also raised complaints about not receiving email notifications.  Some of the users that have raised complaints have both standard and elevated privilege, or administrator domain accounts. 

Your SharePoint farm employs Active Directory authentication.  You recently migrated the farm from 2010 to 2013.  When you check the workflow history, you find messages to the affect that the user could not be found.

Discussion

• Description
• The problem involves SharePoint 2013's new username field: as you type a username into this field, it pops up a list of matching user anames.  These names are those associated with the Display Name field of the user's Active Directory account.
• It so happened that some users with both standard and administrator accounts had identical display names.  Thus, when a user was selected for a list item or workflow, as the user's name was typed in, the first item that popped up was not the standard account but the administrator account, which didn't have an email account configured.
• Solution
• For those users with both standard and administrator domain accounts, ensure that the Active Directory Display Name field provides some indication of which type it is.  For example, you might want to append Admin, OU, LA or some other indicator to the display name of the user's administrator account. This way, when that user's name is entered into a username field, both the user's standard and administrator accounts will appear in the popup, but they will be distinguishable from each other.

References

• TIP: Remove domain from username in SharePoint 2010
• User not receiving Sharepoint emails

Notes

• This was eventually found to be a trivial issue, but when it initially occurred, it had us all scratching our heads.  Ultimately, the cause of the problem was identified through careful and exact observation of how usernames were entered.