You can rewrite almost anything using your mailserver. For instance in postfix, see:
https://serverfault.com/questions/344104/rewrite-from-address-of-all-outgoin...
However, I have found that this doesn't work in a practical sense a lot of the time because spam filters and blacklists notice it -- reverse name resolution doesn't work.
I run a very small mailinglist for forensic pathologists to allow them to discuss cases anonymously. Since many of our cases can have political burdens (e.g. George Floyd), and because of the current political climate in the US, we sometimes cannot speak freely when discussing cases -- and it's important to get "curbside consults" on difficult cases. So I set up an anonymous mailinglist to allow those discussions without as much fear of being persecuted.
My solution has been to go to one of those vendors who will rent you an anonymous vps, buy it with cryptocurrency, get an anonymus domain name (for instance from najalla.la), and set up a server there. My current server is supposedly owned by some name in Turkey. The practical downside of this is that you have to be careful which vendor you use. I got my first server from a vendor that was fairly notorious for supporting spammers, and I found that my ip address was on a number of blacklists -- not because of what *I* had done but because servers on nearby numbers had been spamming and blacklist services now often block broad swaths of numbers on either side of the offender. Thus, if 1.2.3.4 is the spammer and I am at 1.2.3.101, I will still get blacklisted. Yahoo, gmail, att, bellsouth, and others are *very* restrictive.
In order to get around *that* I ended up relaying from my anonymous vendor through one of my non-anonymous servers. Some isps will also block mail that is relayed as well, though.
In fact, one of my not-anonymous servers was a vps hosted by bluehost. I found that I could not even ping or ssh one of my anonymous servers from there. I opened a ticket and found out that the entire class C address range had been firewalled by bluehost.
For awhile, I had aserver on the onion network, and routed my mail:
anonymous clearnet -> onion site -> anonymous clearnet -> users
But -- I'm not sure onionmail is worth the work. It was exhausting to set that up and get it working. I took it down after a few months.
I strongly suggested to my users that they get anonymous email addresses from places like protonmail, whch are sometimes also less restrictive when it comes to blacklisting. Unfortunately, many of my users are not very sophisticated, and insisted on using things like gmail or yahoo.
So, in the end, I had to tailor my relaying and routing for each of the major ISPs. Mail to users from my anonymous site that went to bellsouth went through a different process than those who went to gmail recipients.
Finally, remember that no matter what you do, you will always leave *some* breadcrumbs. One of the nice things about some of these anonymous vps vendors is that you can destroy and create servers on a whim. So, I close down old servers and open up new ones every few months, and transfer the mail service from machine to machine. It requires having disposable domain names and such, and making sure users whitelist them, but they are now a dime a dozen as long as you don't mind having nonsense names.
billo
On Tue, 2023-05-09 at 11:00 +0200, Roland Miyamoto via Mailman-users wrote:
Dear community,
Could anyone tell me whether there is a way to hide the sender address of list mails completely from the recipients.
Even for an anonymous list, the sender still occurs in two fields
envelope-from <sender@sender-domain.tld> X-MailFrom: sender@sender-domain.tld
of the mail header. Is there a way to suppress this information?
Best wishes, Roland
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