You can easily prevent domain aliases and nicknames from showing in Google Contacts by altering a setting in your control panel.
If you have access to the Google Apps administrator control panel you can stop nicknames and domain aliases from appearing in Google Contacts and your Global Address List. Doing this will also remove nicknames and aliases from any auto-complete email lists for your domain.
Once you are in the control panel follow the steps below:
Click on Apps
Click on Google Apps
Choose Contacts from the Services menu
Select Advanced Settings
Select Hide aliases under Choose which user email addresses should be visible to other users
Note that “Changes to contact sharing options may not take effect for up to 24 hours.”
Let us know in the comments below if this Google Contacts tip works for you.