How to stop spammers from sending spam as me

Solution 1:

Short Answer: You can't.

For more info, this gives a basic explaination as to why.

This shows how easy it is to do. It's just the nature of SMTP, it's insecure!

Just because an email appears to come from somebody, it doesn't mean it did.

Solution 2:

You could set up SPF records for your email domains, however this will only have a limited effect, if any.

Solution 3:

Tech support is wrong. There is nothing you can do to stop someone else sending email as if it came from your account(s). Only the receiving system can do anything about it. Measures such as SPF, DKIM and the like help the receiving systems validate senders but such things are not a requirement by any standards and those systems which enforce such things are in fact very broken.

If mail systems did proper checks of the headers to determine whether or not the sender address has been spoofed they could either send an NDR or just quietly drop it based on the results. This wouldn't have any effect on the problem of sender spoofing but would stop us receiving NDRs for messages we didn't send.

For now, just get used to it. It's a normal part of daily life on the Internet and is unlikely to go away any time soon.