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: 465
Connection Security: SSL/TLS
Authentication method: 'Normal password'
Username: Your e-mail address
