How should the SENDER header be used in Emails

I've got a web app which I'm sending emails from. I want the emails to appear to come from users of the system开发者_如何转开发, but guessing that these will appear as spoofed emails as they aren't coming from where they are saying they come from.

I've looked around and it appears that the SENDER header fits the bill. Is this a good solution? Also which way round should it be used? SENDER is the users email? or SENDER is the an email address from the domain I'm sending from?

Thanks in advance

Dave

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Who is doing the sending of the emails? From your description I would guess that some action of a user triggers sending an email. In that case, the user's email address belongs in the From header, and in any case, an email address for your web app should be in the Sender header because that is doing the actual sending of the email.

Of course, this is how it ideally works. I have encountered broken email programs that actually use the Sender header for replies if that is present instead of From, so if the receivers of the emails start replying to you, you will probably need to reconsider, but for now go with the "correct" approach.