We have the same issue. Our groups provides domains/websites/email accounts for 15 companies, 30 domains, and over 100 email addresses. We use some email by Securenym (SquirrelMail) Gmail, and Yahoo. However, half of our 100 email accounts, about 50, are GoDaddy, and we had them all set to SquirrelMail. This was apparently a CPanel decision, and perhaps not a GoDaddy decision. See the differences between "SquirrelMail", or "RoundCube" or "Horde". See - -
In CPanel version 78 (current) they dropped Squirrel Mail. In the older CPanel version 72 (just for example) you can choose between "SquirrelMail", or "RoundCube" or "Horde". We may have to go back from CPanel to WorkSpace on GoDaddy, or rent our own server slice and load either CPanel version 72 or 74. I suppose that GoDaddy had no choice, it was up to CPanel, and you and me, the paying consumers, were given no choice.
A do-it-yourself fix - -
How to keep SquirrelMail after removal - -
The wonderful folks ("quiet cough") at CPanel said - - "..We understand that SquirrelMail’s faithful fans will not welcome this decision, but we have good news! You can continue to use SquirrelMail after version 78 because cPanel & WHM supports custom webmail applications. Follow our documentation on Integrating Custom Webmail Applications, and get the code from the SquirrelMail website..."
Thanks for the helpful response, @IronWorker. However, this option wouldn't work on our shared cPanel accounts as you wouldn't have the necessary access to complete the steps outlined. As the link from cPanel explains, SquirrelMail is no longer supported because it appears to have been abandoned and presents security risks. If you wanted to continue using it, you'd need to move to something that is more configurable, like a VPS or Dedicated Server. Not all customers have received the upgrade to cPanel 78 yet, which is why this has happened to some only recently. However, eventually, all accounts will be on this version. Sorry