[Gyongyos]

I would recommend you to build a custom script to deal with incoming e-mails from your clients. By directly displaying the e-mail address on the site you better build a contact us page with anti spam features (Strong captcha, "Are you human question?") and to delete all e-mails that don't come from your clients instantly after they are inserted in the database. (For example set up a cron job and run it each 10 minutes, check if the e-mail address of the sender is between your clients if yes send the e-mail to your e-mail address else simply delete it from the database)

Before accepting my suggestion change your e-mail because probably many spammers have it already so this solution will won't stop them if you don't change it.

At least this solution helped me and after implementing this I never got a single spam e-mail.