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Is there a way to do a simple validation (a whitelist check) on the email sender before it gets forwarded to the whole group? That way if the sender isnít in the whitelist the email wonít go through?
Like I said earlier I set this forwarder up via the control panel of the hosting account. The server is running apache, and supports PHP, Perl & others. I donít want anything complicated (such as a mailing list), just the ability for anyone in the group to email a single address and that email will be forwarded onto everyone within that group.
Thanks for your help
I don't think you'll be able to do much.
The script (or whatever) you'd have to write would have to connect to the sending domain's MX servers (DNS lookup -- oft times are not valid), try to send an email to them, in the hopes that the domain's mail server rejects the email right away (no such recipient), rather than accept it and store it, or later return a "Recipient unknown" email to the source address.
Pretty nasty, complicated, and VERY time-consuming stuff (in terms of SMTP transaction length)... I've tried to think of a way around that sort of thing as well, but it's near impossible, AFAIK. :(
Another of the big problems is roaming users. If you've got someone who connects from a hotel in Singapore instead of their home in Seattle, their email address would be fine, but the mail server would not be.
So, accomodating roaming users, you could just accept the valid From address ... but it's less than child's play to set up an emai client to send From and Reply-to headers that match your list in the group.
If it were easy, it would have been done by now, probably.
What I really need is a way to verify that the senders email is apart of the 30 or so emails I have already in a group. So far email spoofing hasnít been an issue, so all I would need to do is to compare the senders email & if it is a member of the group (on my email whitelist), then to allow the email to be forwarded on. If it isnít on that listÖ then to reject the email.
That doesnít seem nearly as complicated. Iím just not entirely sure how to go about doing it. Perhaps via a script?
Thanks for the help so far.
Check out Milter.org [milter.org] for more assistance with that. (You do need to be running sendmail.)