Thank you for reaching out to Constant Contact API Support.
It sounds like you have an Automated email set up to send whenever someone is added to a list. What I see as a possible problem with your flow is that Constant Contact will only send an email campaign to a contact once. If you have someone sent the Congratulations email when they are added to the list, if you later remove them and add them back on, our system will see they already got the email and not send it.
If you wish to send that email to them again, it would need to be a different campaign. You could in theory create a new Automated email campaign that is the same as the Congratulations email, and apply it to a new list for those who were in your 'Divorced' list (e.g. 'Re-married'). Then anyone put into that new list is again sent that Congratulations email.
If you need assistance setting up an Automated campaign or contact lists, our main support team is available to assist. Please let me know if you have any questions!
Regards, David Bornstein Tier II API Support Engineer