A common question from my Mailchimp clients is how they may avoid any of their email campaign landing in their subscribers spam or junk folders. Unfortunately there is no means of totally removing the chance that the EDMs will land up in a spam folder but the chance can be minimized.
The issue at hand is that there are very many different email spam detection methods and software that organizations use and it isn’t possible to know and address the tens of millions of variations in factors that spam software use. As an example, with Microsoft Exchange Online you can determine various factors that determine what a spam email message contains.
There are three basic ways of minimizing the chance of your email campaigns going to spam/junk:
Let’s remember Mailchimp actually don’t support custom SPF, they always use their own domains in the sender-envelope.
When they ask you to configure SPF, they should actually be writing SenderId.
More on SPF best practice here: https://www.m3aawg.org/sites/default/files/m3aawg_managing-spf_records-2017-08.pdf