I create some package and set one or more owners for them.
After a commit occur in Phabricator an audit is triggered for the relevant package. It should (I think) send a mail about the commit/audit to the author and the package owners. The author get the mail but the owners not.

/opt/phabricator/bin # ./mail list-outbound
...
977 Sent rXXX: xxx
978 Void rXXX: xxx
...

/opt/phabricator/bin # ./mail show-outbound --id 978
PROPERTIES
ID: 978
Status: void
Related PHID: PHID-CMIT-4lmotodz77hpmxkfspaq
Message: Message has no valid recipients: all To/Cc are disabled, invalid, or configured not to receive this mail.

PARAMETERS
subject: rXXX: xxx
from: PHID-USER-hu7jf4chlb2bty37kg5v
subject-prefix: [Diffusion]
vary-subject-prefix: [Committed]
thread-id: diffusion-audit-PHID-CMIT-4lmotodz77hpmxkfspaq
is-first-message:
exclude: []
mailtags: ["audit-commit"]
is-bulk: 1
to: ["PHID-OPKG-izvkzzwiyvgdx5eprfed"]

HEADERS
Thread-Topic: Commit rXXX
X-Herald-Rules: none
X-Phabricator-To: <PHID-USER-hu7jf4chlb2bty37kg5v>
X-Phabricator-To: <PHID-OPKG-izvkzzwiyvgdx5eprfed>

RECIPIENTS
! PHID-OPKG-izvkzzwiyvgdx5eprfed

• This PHID type is not mailable.

...

This says to me that the the PHID-OPKG-izvkzzwiyvgdx5eprfed recipient is the package id but the phabricator's mail can't resolve this to the real mail addresses of the owners.
What did I wrong?