Squirrel Mail is no longer supported or installed in the latest cPanel/WHM v78 updates. We are not going to be re-installing it manually and will stick with the stock cPanel/WHM setup.
If some users are missing Address Books they can be retrieved in their RAW format using the File Manager in cPanel.
In File Manager, click the settings icon and enable “Show Hidden Files”.
Go into the “.sqmaildata” folder.
The .abook files are what you are looking for.
Once the is downloaded and opened, it will be in a format that is not importable to RoundCube or Horde, which are the other two Webmail options for hosted email customers on linux1.hccl.net or host2.hay.net. These addresses will need to be put in manually. After they are put in, it is recommended that the user export a copy of their Address Book. This export will be importable should they ever need to do that.