Kentico 11 eNewsletter issue

Message: These columns don't currently have unique values.

Exception type: System.ArgumentException Stack trace: at System.Data.ConstraintCollection.AddUniqueConstraint(UniqueConstraint constraint) at System.Data.ConstraintCollection.Add(Constraint constraint, Boolean addUniqueWhenAddingForeign) at System.Data.DataTable.set_PrimaryKey(DataColumn[] value) at CMS.Newsletters.EmailQueueManager.FillContactTable(DataTable table, IssueInfo issue, Int32 siteId, Boolean monitorBounces, Int32 bounceLimit, HashSet1 generatedEmails, IEmailAddressBlocker emailAddressBlocker) at CMS.Newsletters.EmailQueueManager.GenerateContactEmails(IssueInfo issue, SiteInfo site, Boolean monitorBounces, Int32 bounceLimit, HashSet1 generatedEmails, IEmailAddressBlocker emailAddressBlocker) at CMS.Newsletters.EmailQueueManager.GenerateEmails(IssueInfo issue) at CMS.Newsletters.QueueSender.Execute(TaskInfo task)

Are you doing this via the Kentico UI or via the API? If you're doing it via the API, there's a good change you are not properly sending the right data to the methods.

via kentico interface, not API The newsletter subscribe list can't have dup emails?

And the last enewsletter went out in December works, not sure what happened

A subscriber contact/email should technically be in a list exactly 0 or 1 times. The system should handle this automatically and only allow 0 or 1 times per contact/email.

no, I found lots of dup emails in the table Newsletter_Subscirber table, the system doesn't seem to prevent dup emails

If you're using the OOTB subscription form it does or should. So maybe check for duplicates and remove them from that newsletter.

Maybe you could filter it using a global event before sending... see https://docs.xperience.io/k11/custom-development/handling-global-events/reference-global-system-events#ReferenceGlobalsystemevents-NewsletterEvents