JMAP Identity/set rejects group email addresses for group members

[siennathesane]

Issue Description

Group members can send as a group email via SMTP (fixed in #485) but JMAP Identity/set rejects the same address with "E-mail address not configured for this account". This prevents JMAP webmail clients (Bulwark) from replying as shared mailbox addresses.

Expected Behavior

Identity/set should check group membership the same way must-match-sender does.

Actual Behavior

No response

Reproduction Steps

No response

Relevant Log Output

No response

Stalwart Version

v0.15.x

Installation Method

Docker

Database Backend

PostgreSQL

Blob Storage

PostgreSQL

Search Engine

Internal

Directory Backend

OIDC

Additional Context

No response

I acknowledge that:

• I have reviewed the documentation and FAQ and confirm that my issue is NOT addressed there.
• I have searched the Stalwart repository (both open and closed Discussions and Issues) and confirm this is not a duplicate.
• I have set the logging level to trace and included relevant log output if applicable.
• I agree to follow the project's Code of Conduct.