How not to migrate an email domain
It's still a bit of a work in progress, but unfortunately I didn't find great resources on migrating my email over to the new domain. I'm a bit fuzzy on whether you actually have to send out those emails or not, but everyone does it and it seems like a best practice to send out notices for major account changes. Still, with over 300k signups there are a bunch of bogus and deactivated emails in there. My normal mail system handles this pretty gracefully - after a hard bounce or a spam complaint, you go into a bucket of users who will never get another newsletter or automated email again. To make matters worse, my newsletter algorithm prioritizes sending emails to more recently active users first. After an initial burst of "Good" emails, I started hitting around a 5% bounce rate and Mailgun gave me the ban hammer. The same automated system that booted me out the first time kicked in after around 100 normal emails because I was still over 5% bounce rate in the previous 24-hour span.