There are various methods of connecting to mailboxes on our platform. We always recommend IMAP as that helps keep messages in sync between various devices and our webmail system. This is our recommended configuration for Thunderbird mail clients.

Incoming Server (“Account Settings” > “Server Settings”)

Server Name: imap.stackmail.com
Username: Your e-mail address
Port: 993
Connection security: SSL/TLS
Authentication method: 'Normal password'

Outgoing Server (SMTP)

Server Name: smtp.stackmail.com
Port: 587
Connection Security: STARTTLS 
Authentication method: 'Normal password'
Username: Your e-mail address

If you choose to use domain-branded server names, such as mail.your-domain or imap.your-domain, the secure connection may throw a certificate warning due to a common name mismatch. This can be safely trusted and your connection will remain secure.

We have a video showing the setup process: