Several vendors (SendGrid, MailChimp, SendInBlue) have "transactional" emails (sent via an external program relayed through the vendor) and "marketing" emails (managed in the vendor app through HTML templates). The vendors also have unsubscribe management and build up lists of people who have unsubscribed.
How do you use the unsubscribe information in the transactional mail side? If you try to send to X and they've unsubscribed, does it just drop the email sent to X? If not, do you have to check unsubscribe information in your own app before generating a transactional email?
What are best practices in managing this subscribe information across transactional and marketing applications? I have been searching the web, and I just find guides on how to set up the unsubscribe links (sendgrid, mailchimp, sendinblue) , but not how to use the information properly on the transactional side.
For SendGrid, if someone clicks on a global unsubscribe link, then future sends through the SendGrid transactional email API will drop it. You can see the Drop in the "Activity Feed" after the unsubscribe:
The unsubscribe list can be edited manually (to either add or delete names) through a web UI or an API.
There are also unsubscribe groups if you don't want one global unsubscribe list.
I still don't know the easiest way to integrate two systems, though. Presumably a scheduled job to copy from one system to another.