PostMark does one thing really well -> Improving email delivery.

It's a simple benefit and direct benefit so the website needs to reflect that.

But there's one thing I love about this page than anything else:

They mentioned they improve email delivery and it's up to the visitor to relate to that to actual revenue.

It's 10x more powerful to let the visitor realise the ROI by themselves then trying to justify it too hard, this is one of the RARE examples of this strategy done right.