Hello, I had the same issue. Mine turned out to be Postfix storing a huge number of emails in the mail queue due to a real-time alert that didn't have a throttle set. The server was sending out three emails at a time every 70 minutes, and had nearly 600 in the queue. The alert may be gone, but it has already triggered all of the emails. Check the Postfix mail queue: postqueue -p You will likely see a number of undeliverable emails sitting in the queue: (delivery temporarily suspended: connect to (mailserver)[:4d0:a302:1100::151]:25: Network is unreachable) Clear the entire queue including deferred emails: postsuper -d ALL deferred And that should fix it. ... View more