Condition A: A message utilizes lists from multiple data sources.
Result A: Duplicate emails may be sent as there is no check made against each other.

Condition B: Only one data source type list per message, Imported list is data source type, Any Version:
Result B : For imported lists, de-duplicating will automatically occur. If a single list contains the same email address more than once, the message will only be sent to that email address once.
If there are multiple imported lists being used for one message the same will apply. Any recipients with the same email address on both lists will only get 1 email message.


Post version 6.58 of NetCommunity:

Condition C: Send a unique email to each constituent who shares the same email address is marked under Administration > Sites & Settings > General tab > Email Settings, and you have multiple constituents that share the same email address.
Result C:  Each Constituent will receive an email. If the email includes merge fields, the message for each recipient is unique and populates with that constituent’s information.

Condition D: Send a unique email to each constituent who shares the same email address is marked under Administration > Sites & Settings > General tab > Email Settings, and you have one or more constituents that appear across multiple queried lists in your one NetCommunity list. For example, Jane is in two of the lists and John is in a list. Jane and John share an email.
Result D: Each unique Raiser's Edge record will receive an email address. In this example, Jane will receive one email and John will receive one email to the same email address.

Condition E:  Send a unique email to each constituent who shares the same email address is unmarked under Administration > Sites & Settings > General tab > Email Settings, and you have multiple queried lists or one queried list.
Result E: Only one copy of the email is sent to the email address and any merge fields populate with information for the constituent whose record has been in The Raiser's Edge the longest.
 

Prior to version 6.58 of NetCommunity: 


Blackbaud NetCommunity will prevent sending a duplicate email to the same The Raiser's Edge record. It will not prevent duplicate emails if The Raiser's Edge query contains duplicate records, or if two records have the same email address.

If the message is sent to multiple constituent query lists and the same record appears in more than one list, then only one copy of the email will be sent to that record.

Note: This is only true for queries that contain the same record. If there is a duplicated constituent record (i.e., John Doe & Jane Doe) with the same email address, two copies of the email will be sent. For these situations, you'll want to work with The Raiser's Edge Administrator to clean up duplicate records in The Raiser's Edge.



De-Duplication for Campaign emails:

All email messages are automatically de-duplicated on a per message basis.  Messages are not de-duplicated on a per appeal basis.  Each campaign email message can only have one list attached to it.  The above rules for NetCommunity auto de-duplication of emails with one list attached apply to campaign email messages.

Note: The Duplicate Search function should be utilized when there is more than one target list on the appeal to find duplicate email addresses in the lists.  Search results on the Duplicate Records tab are not dynamic. The records that appear in the grid are those from the last search. Any changes made to target lists since the last search, such as due to reacquiring, adding, and removing, do not appear. To update the search results, click Start to run the search again. If there are duplicate email addresses found in the lists from running the Duplicate Search and they are not removed, separate email messages generated using the lists containing the duplicate email addresses will each be sent to the duplicate email address.   So, two separate messages can be sent to the same email address if the email address is in multiple lists and not removed first.  NetCommunity auto de-duplication does not apply across messages.