s-nail error: cannot configure mailboxes on virtual mail server

I am trying to send mail from the command line as root using s-nail via a SMTP server. I have a bespoke /etc/.mailrc file associated with an account with the login details of the SMTP server. My MTA is Postfix a virtual server with ISPConfig. EVERYTHING WAS working fine until I upgraded from Ubuntu 22.04 LTS to 24.04 LTS Now, when I use s-nail, I get an error: *s-nail: /root/mail/sent: No such entry, file or directory s-nail: Failed to save message in /root/mail/sent - message not sent /root/dead.letter 10/243* I think the problem lies in the way s-nail interfaces with Postfix, in other words how it accesses the virtual mail directories created by ISPConfig. But is could possibly be something else related to the Ubuntu upgrade. I would like it to access directories in a specific UserAcount under var/vmail. How can I make changes to that configuration, which is presumably something that s-nail knows about? I keep regular backups and have confirmed that during the Ubuntu process, there were no changes in the Postfix configuration file.