Simple Mail Transfer Protocol Mail Service.
Not much one can say about it.
However……online assertions (at date/time of this post) of (i) 170 unique searches per month and (ii) advertisers paying up to $11 per click.
Of course – you (or someone you know) may be wanting to run such a service?
Being offered via 3rd party domain service – dan.com
Click To Buy or Make An Offer