My domain has been used for sending spam emails and I am receiving hundreds of bounce back emails which I never sent.
This is called as Joe jobbing. you can read about it more here http://en.wikipedia.org/wiki/Joe_job
I tried setting SPF records and validate them with my hosting provider but it didn't work. The request a quote form of my website is not working as well because of the same problem.
If you have the right solution/ process to prevent this please bid on this job while quoting the right budget. (fixed or hourly)
I expect the solution to be effective and problem shouldn't come back.