<div dir="ltr">This one is going to be tough. It would be best to do this at the MTA and not in SA since SA only works with the visible From: (header) address and not the envelope-from that the MTA has access to. The envelope-from is what SPF checks and DMARC checks the visible From: header.<div><br></div><div>Assuming that all legit mail from your own domain comes from trusted/internal networks by your MTA, you could put a block on the envelope-from address having your own domain. In Postfix this is fairly easy since you can order the checks the way you need them. Standard practice is to allow your networks first then do sender checks later which would handle this scenario.</div><div><br></div><div>I switched from sendmail to Postfix about 5 years ago and haven't looked back. So many things that required milters in sendmail were built-in to Postfix. I never liked dealing with the sendmail config file either. Switching from sendmail to Postfix is not that hard to do basic mail flow but it takes some time to wrap your head around the advanced Postfix settings since it's so flexible.</div><div><br></div><div>If you want to look at an example config, take a look at the EFA project which is a prebuilt VM image with MailScanner, Mailwatch, and pretty good default Postfix settings to get started with.</div><div><a href="https://efa-project.org/">https://efa-project.org/</a></div><div><br></div><div>Dave</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Dec 23, 2016 at 3:06 PM, Jason Waters <span dir="ltr"><<a href="mailto:jason@geeknocity.com" target="_blank">jason@geeknocity.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">What do you use for an MTA? I know with postfix you can use some smtp restrictions to solve this problem.</div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Fri, Dec 23, 2016 at 3:00 PM, Philip Parsons <span dir="ltr"><<a href="mailto:pparsons@techeez.com" target="_blank">pparsons@techeez.com</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
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<p class="MsoNormal">I use Mailscanner and Send mail. We have a few instances that we are receiving spam from
<a href="mailto:jack@example.com" target="_blank">jack@example.com</a> to <a href="mailto:jack@example.com" target="_blank">
jack@example.com</a> and it is getting through. I have not seemed to find and answers as to how to stop this? Anyone got an Idea. We already have SPF setup which helps but is not fully for this situation.<u></u><u></u></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Thank you.</span><span style="font-size:12.0pt;font-family:"Times New Roman",serif">
<br><span class="m_-4540665633957088318HOEnZb"><font color="#888888">
</font></span></span><span class="m_-4540665633957088318HOEnZb"><font color="#888888"><span style="font-size:16.0pt;font-family:"Comic Sans MS"">Philip Parsons</span><span style="font-size:12.0pt;font-family:"Times New Roman",serif"><br>
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