After a client’s RSS Feed daily email campaign stopped working I had to reanalyze a series of firewall rules I had just set in their CloudFlare account.

Turns out I was being a little too drastic (which unfortunately was absolutely necessary due to crazy amount of bots that were hitting the server).

Luckily CloudFlare’s firewall logs will show you the requests as they are being blocked so I was able to identify the requests coming from MailChimp. They use the User Agent MailChimp.com and I’ve been able to detect at least two IP addresses: 34.75.225.48 and 34.138.56.119 —In 1 hour of testing I didn’t see another one but of course that’s not to be taken as “conclusive”.

For now I have created an additional firewall rule to Allow requests from MailChimp by using the User Agent as filter. Of course… this can be easily faked so we’ll have to keep an eye on it.

I’ve reached out to their support team to get a list of all IP addresses used. Let’s hope I’ll be able to update this soon.

Update

Three months later, I have not heard back from MailChimp's support team but luckily the rule in place has been working wonderfully!