Webmailer
You'll find the webmailer at the following URL:
https://webmail.herzlieb-it.de
Login with your email-address (NOT your alias, if any!) and your given password.
Besides the email-client you may change the settings for your email-account here (Name, password, autoresponder, forwarding ...).
Email client
The following settings apply to your email client (e.g. Mozilla Thunderbird). The mailserver uses a paid certificate for encryption. The email client should be able to establish a secure connection to the mailserver out of the box.
Set the incoming server to: IMAP
Incoming server (IMAP): imap.herzlieb-it.de
Security: STARTTLS
Port: 143
Authentication: Normal Password
Username: Your email-address
Password: Your given password
Outgoing server (SMTP): smtp.herzlieb-it.de
Security: STARTTLS or TLS
Port: 587
Authentication: Normal Password
Username: Your email-address
Password: Your given password