Login:

Username: Their full email address
Password: Their password

Ports:

POP3 Non-SSL: 110
POP3 SSL: 995
IMAP Non-SSL: 143
IMAP SSL: 993
SMTP Non-SSL: 587
SMTP SSL: 465

Server Names:

All Non-SSL: mail.customerdomain.com
All SSL: mail.customerdomain.com *OR* lb1.yourwebworkspace.com
Obviously swap out “customerdomain.com” for whatever the customer’s actual domain name is.
The outgoing mail server requires authentication, and username/password are the same as the incoming mail server.
If the mail.theirdomain.com server name doesn’t work, switch to lb1.yourwebworkspace.com – but the preferable way to configure it is the former.