Issue Description
When adding recipients to a mailing list that exist locally, but you add a sub address with +test (domain is enabled for sub-addressing) the mails are not delivered to the local mailbox and instead are bounced with 5.5.0, Message: Mailbox not found.
Expected Behavior
The email should be delivered to the user mailbox with the sub address so the user can perform additional filtering or sieve scripting. NOTE: I am aware that you can also achieve this via to header that will be mailing list. However, it feels weird that these sub addresses are bounced while sending directly to this address does work.
Actual Behavior
For each local recipient with a sub address the message is rejected with 5.5.0, Message: Mailbox not found.
Reproduction Steps
- Default stalwart setup
- Create a domain with sub-addressing enabled (default)
- Create an account
- Create a mailing list with the account from step 3 and add the account from step 3 with a sub address as recipient
- Send email to the mailing list
Relevant Log Output
stalwart-6c7cfdbd76-wv562 2026-08-10T20:30:45Z INFO DSN permanent failure notification (delivery.dsn-perm-fail) queueId = 323200149343964161, queueName = "local", from = "[email protected]", to = ["[email protected]", "[email protected]", "[email protected]"], size = 9680, total = 5, to = "[email protected]", hostname = "localhost", details = "Unexpected response for RCPT TO:<[email protected]>: Code: 550, Enhanced code: 5.5.0, Message: Mailbox not found.", total = 0
stalwart-6c7cfdbd76-wv562 2026-08-10T20:30:45Z INFO DSN success notification (delivery.dsn-success) queueId = 323200149343964161, queueName = "local", from = "[email protected]", to = ["[email protected]", "[email protected]", "[email protected]"], size = 9680, total = 5, to = "[email protected]", hostname = "localhost", code = 250, details = "OK"
stalwart-6c7cfdbd76-wv562 2026-08-10T20:30:45Z INFO DSN permanent failure notification (delivery.dsn-perm-fail) queueId = 323200149343964161, queueName = "local", from = "[email protected]", to = ["[email protected]", "[email protected]", "[email protected]"], size = 9680, total = 5, to = "[email protected]", hostname = "localhost", details = "Unexpected response for RCPT TO:<[email protected]>: Code: 550, Enhanced code: 5.5.0, Message: Mailbox not found.", total = 0
Stalwart Version
v0.16.x
Installation Method
Docker
Database Backend
PostgreSQL
Blob Storage
PostgreSQL
Search Engine
PostgreSQL
Directory Backend
Internal
Additional Context
External recipients with a sub address works fine (which makes a lot of sense).
There might be some links with Domain aliases not (automatically) working for mailing lists for said domain
I have reviewed the documentation and FAQ and confirm that my issue is NOT addressed there.
on
I have searched this support forum (open and closed topics) and confirm this is not a duplicate.
on
I understand that topics in this category are triaged by a bot first but a human reply will follow up. If I’d prefer a human-only reply, I’ll add the no-ai tag to my topic.
on