Use MiaB to send as third-party forwarding email?

[gwhitney]

I have a permanent, third-party forwarding service that I like to use, and I would like my emails to appear as if they are “From:” that address. This seems legitimate to me, because it is an email address that was granted to me by the third party, and all email to it does forward to me. How do I set this up with MiaB? What follows is what I have tried so far.

For the discussion, let’s say that the third party address is “gwhitney@mail.xxxx.edu” and my MiaB box.yyyy.com is the nameserver and mail exchanger for domain yyyy.com.

I set up an alias on my box of the form “gwhitney@mail.xxxx.edu forwards to glen@yyyy.com”. Sure, that puts a bunch of A and MX records for mail.xxxx.edu on box.yyyy.com, but who cares, nobody is asking box.yyyy.com about the IP addresses for mail.xxxx.edu.
Once I have done that, my email client will happily send a message from gwhitney@mail.xxxx.edu with the smtp server box.yyyy.com using the username and password for my account on box.yyyy.com. But the problem comes because they are DKIM signed with
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mail.xxx.edu;
s=mail; t=1478812475;
bh=RHI91NDg1Go8f6isolS2HCe2tXiflhd+gsgHAECfFTU=;
h=To:From:Subject:Date:From;
b=fu5vCOydmDigd9J1Ry9/rcKbEhh1X02wf2PhhAe4rvZLtYCwDFc5UmIxdniElMdLL
oMIXPaeV9XHSfDnreHL3tloBAOS/z4LMw3b4gQJUKcUxdbeRnfwKIFooJk4oie26oa
JIS7BgBqp0BXaFI9aOFb6w1E0vCYamR/sOacLRuCT4TACRWZIEuMUXkI1gnRd9YE+8
6KME4rSFEdEjNiBidHDu4BzIVQvBK3QccIzdzlclTedfwtx4vDN1UADgQvVxGs0X4f
pa7zVSYwM3lAt+NksBLMCj5qI7m7fL4KYgRvx0j7b8GDcKsNzWpmKhTe/+ICdn1sJ6
qvu19i3pV1cYg==
which is not a valid signature because I of course have no way of putting records on the real mail.xxxx.edu nameserver to match this signature. So now I have an invalid DKIM signature in my email, which is a huge spam no-no, and hence my messages are bounced from everywhere.
Interestingly, I can add gwhitney@mail.xxxx.edu as a “send from” address on a gmail account, and then the messages from gwhitney@mail.xxxx.edu via gmail come through with this header:
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=1e100.net; s=20130820;
h=x-gm-message-state:mime-version:from:date:message-id:subject:to;
bh=GEmKff8jfNdnsZi8v7W5+97r/fhefh27wDuMkrw7tsI=;
b=TjDVICyECyOLFzjBbb2UE6lIIx2NG0Xf+yKxg72A+fmobmCqJoETadiPmjyG2atNlI
DyCco+qOddPFzsAV/BnkWpx9qCdHoY/TTQOgtiVXRSr+BrYib0Do9l61fne2ZhROZl45
yKRo7o+Hsv8Z+uNO/V+AJzyHgifSv2HqpvqVFWztvgSxDeoS56mLTSfsqmuukpQ80r7k
jORbIwJZ+AN3D9W9xK/9j43MF4ZqVjStFdBje6Po3g230nSSs2cfVYQVXdIUus11QnWI
CqzxknIww1tpNtU0W9hlMQs2Rzc50+JdVXHMlEexMszImFBKhRuiz6K+7UQWNKJVdXju
yU4w==
and although they still get a small demerit for not being DKIM signed on the spam tester websites, they do not get marked as spam by most recipients because not being DKIM signed is a much less bad offense than having an invalid DKIM signature.

How can I configure MiaB to not generate DKIM signatures, or to change their headers like Google does, to be able to send email from gwhitney@mail.xxxx.edu via MiaB without their having invalid DKIM signatures?

Thanks for the help.

[bronson]

Generally, the best way to make it appear as if your email is from a third party is to actually route it through that third party. You can configure Postfix to do that, it’s called a satellite system. (MiaB doesn’t actually support that configuration, so you’ll be out in unsupported modification territory, but it’s at least doable).

And, since you call them a forwarding service, this sounds like it should be pretty easy.

If you can’t do that, then technically you can have your MiaB send the email directly… Problem is, you’re going to have deliverability issues since there’s no good way for recipients to tell your messages apart from spam. You’ll need to collaborate with your forwarding service.

If you still want to do that, you would start by managing your DNS externally (maybe through your ISP), and not including SPF/DKIM/DMARC records.

[gwhitney]

Sadly, mail.xxxx.edu’s explicit policy is to not let its registered users send outgoing mail through its servers; it merely forwards incoming mail to me. So I need to do the best I can to send the mails myself. What I’ve done at the moment is remove the forwarder from mail.xxxx.edu to yyyy.com in MiaB, and then manually edit the mail.cf to remove the flag diallowing login-user/sender mismatch. That’s working OK, but yes, a few recipients are balking. Is there anything better than this that I can do?
Thanks, Glen