Can a mail-sending program send mails under my email?

I'm new to SMTP techniques so with just a few days work with it, I have this question - Can a mail-sending program send mails under my email?

It seems like I can put any email in to from field and if I put my friend'开发者_运维百科s email there, I can disguise him!? This sound strange since I believe that being some one else is not that ease at all.

Please guide me if you have experiences on this.

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Any email client can send an email using ANY email address as the from field.

That said, a lot of receiving mail servers are configured to do various tests to ensure that the email is coming from a real mail server.

For a list of those techniques used by receiving mail servers go here: http://en.wikipedia.org/wiki/Anti-spam_techniques Specifically the "automated techniques for e-mail administrators" section.

A short list from there is:
1. Reverse DNS - tests the IP address of the sender to ensure that the IP is listed as an MX record for the domain.
2. FCrDNS - receiving mail server will attempt to do an SMTP HELO or EHLO command back to the sender's IP. This makes sure the sender is an SMTP server.
3. Disallow Dynamic IPs - receiving server will test the sender's IP to see if it is DHCP'd. If so, then the mail is marked as spam.

Point is, you can send email as being originated from any email address. However, there is a huge possibility that the email will simply be deleted by the receiving server.

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Actually, you can do what you say with an email client like Thunderbird where you can set the From address freely.

Anyway, you will need a SMTP server that will accept this any domain address (your provider SMTP will probably do).

That's also why some SMTP servers (like Gmail's one for instance) force the user to get athenticated and displays his user adress (it will sometimes display on behalf of when sending from another e-mail address. This is very well explained on Google site.

Regards,

Max