Philip Bondi writes:
[E]mails from banks, government, ecommerce or other important providers are distributed to multiple family members.
This an interesting application, but very likely to have delivery issues because most financial institutions participate in the DMARC protocol to control use of their domains in email. I would guess that government and ecommerce do as well, but my personal experience them is using the web or bespoke apps. Since you're stripping the From header field, you shouldn't have DMARC issues, but many providers are more aggressive than the DMARC standard recommends.
Do you struggle with "message rejected. AUP#CDRBL" while using mailman with your ISP email relay?
The code "AUP#CDRBL" is specific to your ISP. USers of other sites won't know what that means. You should check the rejection or the ISP's pages for a page explaining the code. Also, there are numerical codes like "503" and "5.7.1" (it will probably start with 5 because that's the code for "this message cannot be delivered"). The standardized codes are not at all specific about why the ISP doesn't like your mail, but some ISPs also add more specific reasons in a comment field immediately after the numerical code.
"AUP" very likely stands for "Acceptable Use Policy", which is standard terminology for your side of the agreement with the ISP. I don't know what "CDRBL" means. "RBL" is a common acronym for "realtime block list" which is a system where the source domain or IP is looked up and checked against a list of spam or phishing sources. That seems unlikely, though, because normally these are based on the IP address of the most recent connection---which would be yours.
On mailman2, I mitigated by stripping headers, wrapping message and DKIM signing. Here is a mailman2 message that is stripped, wrapped and signed.
If that works, all of those features are at least as well supported by Mailman 3 as by Mailman 2. I don't see why you'd have more problems with Mailman 3 than Mailman 2 if you use them same settings,
The only additional possibility that you haven't mentioned (but may already be using) is to set the list to anonymous.
This is almost useless, it just confirms what you said in the text. If that's not working, we will need to see the raw email to help you, including the entire header and maybe the body. If you're not comfortable sending to the list (and for this data, maybe you should be uncomfortable), you can send to me and Mark at our personal addresses.
Steve