The best thing here is to set up a header filter that replaces first From: header with your adress, and first To: header with the destination gmail adress. To prevent that any spam blacklisted adresses appear, discard every to: and cc: header after this. Then you ensure the MAIL FROM in the SMTP communication with gmail, states your adress and not Yahoo’s. Add a SPF record to your domain, and then you are done.
If you want to go the encapsulation way, it gets a little bit more complicated, and you need some sort of milter or post-processing filter to encapsulate the email. From: Il Neofita Sent: Thursday, September 17, 2015 8:12 PM To: Sebastian Nielsen Cc: postfix-users@postfix.org Subject: Re: Forward rejected by yahoo Thank you very much for the fast reply. I was looking on sieve or postfix and I do not find how I can do it. Since I believe that will be the best way to do it. Can you help me out? Thank you On Thu, Sep 17, 2015 at 1:51 PM, Sebastian Nielsen <sebast...@sebbe.eu> wrote: No. SPF is designed to be secure, eg you cannot add some header to bypass the authentication, then every phisher would add such a header. What you need to do, is to rewrite the FROM adress or encapsulate the email. Rewriting FROM adress can be as simple as rewriting yourn...@yahoo.com to yourn...@yourserver.tld , or even yourname.yahoo....@yourserver.tld Then you host a own SPF record. The disadvantage of this method, is that it will not be possible to reply or answer on emails from your google account. You could however, since you know the domain and username, manually write the correct @yahoo.com adress in the “to” field when replying to a email. Another way, is to encapsulate the email in a new message/rfc822 container, where the outer container contains like From: forwar...@yourserver.tld To: somen...@gmail.com , Subject: Fwd: Original Subject And then the inner container contains: From: yourn...@yahoo.com To: yourn...@yourserver.tld Subject: Original Subject The advantage with this method is that you can reply to the email by replying to the inner container. This is how most email clients forward email, by encapsulating them. In most cases, a email client will either show a iframe showing the original content, a button to open the mail in a new window, or a attached file that can be opened to show the mail. Of course, its important that you do publish a own SPF record. And also, its a bad idea to forward spoofed email, since this could get your domain “blacklisted” at google, thus its a good idea to SPF and/or DKIM check any incoming email on your forwarder adress before forwarding them. From: Il Neofita Sent: Thursday, September 17, 2015 7:40 PM To: postfix-users@postfix.org Subject: Forward rejected by yahoo Hi, I have the following problem if I forward an email received from yahoo to an other yahoo account the message is rejected. If I send a message from yahoo -> my server and forwarded to a google account the message is marked as spam, since is considered a spoofed. Can I fixed this adding some header? Thank you
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