How can I prevent invalid e-mails bearing my domain name?

e-mails are currently going around, with an e-mail address that bears my domain name. How can I prevent this? I have checked and there is no such e-mail address on my exchange server 2003. I have a sonicwall firewall NSA 3500.
bobox00Asked:
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Peter HartCommented:
someone has hijacked your email name - its very easy to set up an email with a fake (or someone elses) email address as the return address, this enables spammers to flood the market and the return addresses get the flak
to stop emails being recieved for unknown users:
on your exchange you can configure the catch all email to simply reject unknown email addresses.
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war1Commented:
Hello bobox00,

Make sure your computer is not an open relay
http://www.postcastserver.com/help/Blocking_Open_Relays.aspx
and
http://support.microsoft.com/kb/324059

If you have control of the server, you can Integrate SPF and DomainKeys, which would help to stop spoofing in the future:

SPF:
http://www.openspf.org/

DomainKeys:
http://domainkeys.sourceforge.net/

Hope this helps!
war1
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bobox00Author Commented:
Will a security certificate help prevent people from using my domain name to send e-mails illegitimately?
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TolomirAdministratorCommented:
Well the problem with emails is everyone can run a mailer sending spam with any email address.

All you can make sure, as war1 points out is that receiving email servers drop all emails with your sitename that is not SPF signed: http://www.openspf.org/FAQ/What_is_SPF

Still any mailer not using SPF will receive your emails and send them to the associated receivers.

Of cause antispam measures can be still intact.

Tolomir
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maximaalCommented:
We had the same problem.
We installed GFI Mailessentials and followed:
http://forums.gfi.com/Spoofed_SPAM_from_MIME_FROM_addresses_that_SPF-FAIL/m_900759763/tm.htm

problem solved.
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bobox00Author Commented:
Thanks guys.
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