Cannot send emails - address missing domain

Steps to reproduce

1. Install mail app
2. Configure new mail account
3. Attempt to send an email
   In the stated example, an email is sent from 'Sender Name' sender.address@myemail.tld to recipient.address@theiremail.tld

Expected behavior

1. The mail app installs
2. The new mail account is configured and connection with mail server is confirmed.
   3.a. The email should be saved to the outbox
   3.b The email should be sent.
   3.c The email should be moved from the outbox to the sent folder.

Actual behavior

1. The mail app installs
2. The new mail account is configured and connection with mail server is confirmed.
   3.a. The email is saved to the outbox
   3.b. The email is not send. A 'Could not send message' notificaton is presented.
   3.c. The email remains in the outbox. The note 'Mail server error' is stated next to the note.
   The error 'Horde_Mime_Exception Address is missing domain.' is recorded in the nextcloud log

Mail app version

5.1.5

Nextcloud version

31.0.5

Mailserver or service

Gmail

Operating system

FreeBSD 13.3 (jailed)

PHP engine version

PHP 8.3

Nextcloud memory caching

Only APCu

Web server

Nginx

Database

MariaDB

Additional info

In the stated example, an email is sent from 'Sender Name' <sender.address@myemail.tld> to <recipient.address@theiremail.tld>.
As far as I can tell, the attached raw log data for the 'Horde_Mime_Exception Address is missing domain.' error suggests the domain name has been stripped from the sending address.

This is the first time I have installed the mail app, although I have had Nextcloud/Owncloud running without major issue on the same server for 10+ years. Nextcloud (and nginx, and PHP) is installed from FreeBSD's ports tree.
For what it's worth, I'm using Firefox, but can't see how that would be related to the issue.