I’m sorry, but this is an NS7 customization, and it is not handled by the migration tool. To implement a similar customization in NS8, refer to this documentation: GitHub - NethServer/ns8-mail: NS8 Mail module with SMTP, IMAP, Spam/Virus filter
If you introduce a custom Postfix table, such as “canonical,” ensure its path resides under the postfix-custom volume; otherwise, its data will be lost on the next container restart.