If I purchase a domain specifically for email marketing, does this domain need to point to a website for greater email deliverability? Thanks.
It has more to do with trust than deliverability. Your email will be delivered whether you have a website under that domain name or not. But if I got an email from you with no link to your website, I will probably use your email address domain name to check out your website. No website - no business.
We are trying a new service that claims to provide a business with more inbox reach than Constant Contact or other emailing systems. It is because they send it from our own company's domain, instead of from its own. Supposedly, a lot of people have any emails from Constant Contact or other such services sent right to their spam folder. Too early for any conclusions, but I will let you know what we experience. Note that we are only emailing to our inhouse email list of customers, prospects, etc.
If you are going to purchase a domain for email marketing, I would suggest making a simple landing page that collects emails. You can offer a free report or product (find a free one or create your own in a few hours). This used to be the top way to collect emails back in the day but I'm not sure how well it works now.