Not the author, but have some experience with the mailgun api. AFAIK there's no sla/guarantee/redelivery for the webhooks, and they have to be setup for each domain. Looping the account to fetch all logs for the last 48 hours is relatively simple and robust.

OP here (actually, he is my co-founder, same company). I can confirm this experience, looping seems to work.

In our own setup, we fetch data for the last 24h twice a day and then just insert everything. We have a db constraint on the message ID mailgun sends us, so only news ones will be persisted. We aren't even bothered with filtering before inserting, the db constraint does the trick.