Email Opt-out best practices for multiple systems

Hi, 

We are discussing adding another tool for our Sales team to send out templated emails through a more customized cadence. With the addition of another platform, would the best practice be to honor those already unsubscribed through Marketo and not allow them to get these sales emails OR have folks unsubscribe through the new platform if they aren't interested in hearing from sales? If the latter, should they then be flagged in Marketo as unsubscribed? I'm concerned there isn't a legal difference between a "sales" email vs. a "marketing" email. 

Thank you,

Reanna