Dovecot submission proxy constraints

Dear Dovecot experts,

in 2017 Stephan Bosch mentioned in an email about the Dovecot submission proxy [0]:

"The current implementation does require that the proxy has direct access to the user's mailbox for BURL (e.g. by running it on the same host as imap), but that restriction should be resolved soon, allowing for more complex setups."

Is the mentioned restriction (access to mailbox) still valid in 2023 or has this constraint been lifted in the meantime?

Best regards,

Peter

[0] https://dovecot.org/pipermail/dovecot/2017-December/110282.html