Hello @SamDube,
Thank you for your question.
I haven’t personally used Mailchimp, but I did some research and I think the difference might be related to a tool they have called “ReplyTo”. Hubspot doesn’t offer a tool that checks to see if a reply to one of your marketing emails is an Auto-reply or not. To stop these auto-replies from flooding your inbox, you’d have to create filters in your email account to have them go into a separate folder instead of your inbox.
If you’d like to suggest to our product team that a tool like “ReplyTo” be made available in future product release, please feel free to submit the idea at the Hubspot Ideas Forum.
I hope this helps!
Brett