How are people able to spam me using my own site email as the return address? E.G. admin@mysite.com. How do I stop this. I can't have it barred by my email supplier as this would mean not receiving regular emails.
maurellis

Do you have a contact form on your site? Does it have a CAPTCHA or some way to catch robots?

You cannot.

Email is just like a text file. You can put anything in the "from" field.
If you put george@whitehouse.org, then the reply address for that email will be that one.

Here is a typical telnet communication to a mail server (taken live from my workstation and to my mail server)

telnet mail.myserver.com 25
Trying 193.58.255.251...
Connected to mail.myserver.com.
Escape character is '^]'.
220 mail.myserver.com ESMTP Postfix
ehlo me@myplace.com
250-mail.myserver.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN PLAIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
mail from: george@whitehouse.gov
250 2.1.0 Ok
rcpt to: someone@myserver.com
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
blah blah blah
.
250 2.0.0 Ok: queued as C7C8451C001

Spammers use this to send baits, anti-spam filter intercepts them, and reply blindly to the "from" content another message which is very much likely to be considered as spam in my opinion.

I delete them silently personally now. I used to store them in a spam@myserver.com mailbox, but when you get 250 spams per hours, you just don't want to even look at them...