FW: Mail relay question

["Nick Vaernhoej" <nick.vaernhoej () capitalcardservices com>]

Good day,

So I am somewhat green when it comes to how mail gateways manage email.

After finding that my own mail setup at home has caught almost 5000 spam mails in less than a month I have finally 
thrown my hands in the air and wanted to hopefully get some understanding from this list.

The amount alone is huge I think when I am only hosting my wife and myself (as well as the usual abuse etc. contacts).
I am worried that my home is an open relay in a manner I have not found.

Then I learn that via telnet I can send email from mydomain.com to mydomain.com and have it delivered even when the 
telnet session is from a public IP.

So, I am a little fuzzy on what it is I am trying to learn here, but:
1. Would you think 5000 emails a month with maybe 200 valid emails is normal in a home/family type setup?

2. Is mail always accepted and relayed when the sender and recipient domain is the same? (This is without sender 
authentication configured or capability).
        a. If yes, what is to stop an angry neighbor on his vacation to China from sending a nasty email from me to my 
wife? (In this unsecure setup).
        b. My gateway at home (Smoothwall using DSPAM/SEMF? mod) only accepts the initial HELO if followed by 
connecting domain name (HELO domain.com) So how come I can connect from domainx.com and send email from domainy.com to 
domainy.com?
        c. What can I do to remove this risk?

3. Any recommendations on a free mail gateway solution?  SpamAssassin? ClamAV? My goal is to migrate away from Exchange 
2003. I have been wanting to try Zimbra for mail server but would like a good mail gateway in the DMZ instead of hosted 
by the firewall.

Thank you and I will follow up with answers to questions for clarification.

Nick Vaernhoej
"Quidquid latine dictum sit, altum sonatur."

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