From XMission Wiki
- Click , go to Programs and open Thunderbird.
- In Thunderbird, click then Account Settings.
- Click .Change mail.xmission.com to zimbra.xmission.com and ensure your full email address is in the User Name field.
- Click , select mail.xmission.com and click .
- Change mail.xmission.com to zimbra.xmission.com. Check and enter your full email address below.