> This is the first time I hear Mailchimp (or any other company) has some special deal or treatment from ISPs in regarding to their sending emails reputation.
If you use Gmail and PayPal you can see this in action. There will be a little key there. You have to be an approved sender to get the key. The key, besides being a visual indicator, guarantees delivery in the inbox.
Most people who admin big mail sites know each other. When their mail is bouncing, they call each other and ask for help. When they see their friend's big site getting a lot of spam warnings, they call their friend and say "hey this word in your email is triggering our spam filter, you should change it".
I don't use Gmail at all and have only used PayPal perhaps twice in the last three years so I can't be certain but you're not referring to their visual indicators for encrypted e-mail [0], right? You're talking about something different?
If you use Gmail and PayPal you can see this in action. There will be a little key there. You have to be an approved sender to get the key. The key, besides being a visual indicator, guarantees delivery in the inbox.
Most people who admin big mail sites know each other. When their mail is bouncing, they call each other and ask for help. When they see their friend's big site getting a lot of spam warnings, they call their friend and say "hey this word in your email is triggering our spam filter, you should change it".
This is just how industry works.