[Mailman-Users] Redirected email address as entrypoint to mailing list

[Stephen J. Turnbull]

Andrew Stuart writes:
 > Image a mailing list mylist at example.org
 > 
 > Is there any reason why the users could not be told to use
 > adifferentlist at adifferentdomain.org which simply forwards mail to
 > mylist at example.org
 > 
 > Would this raise any potential problems?

Depends on what you are trying to do.  The main issues relate to users
being subscribed to mylist but post to adifferentlist.  Also MTA
configuration may be tricky (SPF, DKIM, DMARC) depending on whether
you have full control of both domains.

Problems with lists:

- This may be quite confusing to users, as they post to adifferentlist
  but set nomail, notmetoo, digest settings etc on mylist.
- This will confuse smart software, because the List-* headers will
  point to mylist.  (Some MUAs are smart enough to reply to List-Post
  by default or when a "list-reply" command is invoked.)
- If the lists are served by different MLM instances, ban settings etc
  on one cannot be referenced by the other.
- There are some settings to alleviate user confusion (sibling lists,
  umbrella lists) which you will not be able to use across instances.

Mailman 3 will help to alleviate some of these issues by making it
easier to serve multiple domains from one instance, but if your
domains are actually different hosts, you're not going to be able to
use those features without substantial extension to current Mailman 3
(as we've discussed on mailman-developers, access to many Mailman 3
databases requires running on the same host).