Hi, everyone! I tried to respond to this question on YouTube, but unfortunately all my attempts to respond were blocked by YouTube’s spam filter so I figured I would post it here…and no, the irony isn’t lost on me 
Last month, we released a new feature that validates email addresses upon manual entry. The popular question from Luke Messecar was,
“If someone from a “non-marketable” email domain signs up on their own using a form and opts into marketing, will they be able to receive it? Or, does the email validation check only opt out contacts from non marketable domains when we manually add them to Keap? Either way, it seems like even more restrictions on our ability to email contacts so I’m not sure how that’s a plus for Keap users.”
The answer is that this feature is a pretty basic email validation implementation that prevents you from entering and thus sending to an “unmarketable” email address. It scans manually entered email address for misspellings (like gmail.vom) and non-marketable domains (blah@wellsfargo.com). Previously, this validation only existed in bulk imports. The gist of this feature is to further prevent unmarketable email addresses from entering your queue and being ultimately rejected, or worse case scenario, being marked as spam from the recipient ISP
You can read about “Opt-Out: System” in our help center: https://help.infusionsoft.com/help/email-status-icons-explained
Future iterations will likely expand this to other areas of the application and may include real-time validation when entering data manually.