This confirms that Stalwart’s mailing list implementation delivers to a set of recipients based purely on address expansion; it does not send a header like To/Cc listing all recipients, and there is no built-in “reflector” mode that exposes the full recipient list to subscribers. The MailingList object stores recipients as a flat list, but the server delivers a copy to each recipient individually rather than rewriting headers to show all addresses.
There is no setting (in the WebUI or via stalwart-cli) to make a Stalwart mailing list expose participant addresses to each other. That kind of behavior (a “reflector” list showing all subscribers in To/Cc, common in classic listserv software) isn’t part of the mailing-list feature as documented; Stalwart’s lists just fan a single incoming message out to the stored recipient set. If you need visible participant lists, you’d have to build that with a Sieve script or external mailing-list manager that rewrites headers, since it’s outside of what the built-in MailingList object does.
Docs reference: Mailing lists | Stalwart
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