The term for this is Hellbanning.
Free dating sites such as Plentyoffish.com or OkCupid.com tend to be flooded with creeps. Creeps here are defined as users who harass others with inappropriate messages.
Most women who have been on these sites have at least one story of a guy sending some ridiculous email with an incredibly offensive suggestion or perhaps an indecent picture attached.
A strategy to mitigate the effects of these creeps is two fold; first, identify these profiles, and second, prevent these profiles from continuing to creep.
An option for the first part would be to create a “creep trap”. Ideally, this would be a profile of a fictional woman with attractive pictures and a generic profile. Messages sent to this profile would then be scrutinized for their quality. If they contained ads, an over the top request, or are written like a text message, the senders profile would be flagged.
As for the second part, I do not think this is taken advantage enough in services such as these. Some sites are diligent and do ban troublesome users, but with the internet it is easy enough to create another profile. Instead, the site can quietly sandbox the user. To them it seems as though their emails are being sent; though, in reality, they are deleted and their profile is not viewable by anyone else.
The specifics of how many creep emails over a period of time should cause a user to be sandboxed is up for discussion, as well as sandbox duration. Overall, I would imagine this would amend the creep problem as well as improve user confidence.