[foxcpp]

Yes, this is possible.

This page shows how to configure maddy to only handle SMTP: https://foxcpp.dev/maddy/tutorials/smtp-only/ You can follow it but swap Dovecot for another maddy instance, configured as shown here: https://foxcpp.dev/maddy/tutorials/imap-only/

This works because maddy implements both client and server for Dovecot's SASL delegation protocol.

Alternatively you can configure pass_table to read from shared SQL database. Hm, maddy-tables(5) man page is not rendered on the website but you can look at sql_query module.