ActiveCampaign's Robert Colomberti's explains.
This is REALLY good stuff. The date range guidance might change depending on your industry or differences in sales pipeline, and the segmentation guidance gets a bit platform specific, but the core of this is solid.
As far as the bit at the end about using an email validation vendor, that's a whole other discussion. Upfront verification that somebody isn't submitting an invalid address into a form is a good thing, but don't forget that it's not the same as verifying permission. Data validation isn't going to fix a non-permissioned list, for example. That kind of thing is still deliverability killing. (I don't mean to imply that ActiveCampaign says otherwise. I am just making my own voice heard here.)