The initial installation hangs. In order to install eM Client, proceed through the normal install process (by searching for em client in CrossOver), and once the install hangs, using the CrossOver app icon in the taskbar, click on that icon and select "Force Shutdown". Then click the eM Client icon in CrossOver, and click the cog wheel icon to install "Core Fonts" into the bottle. Now you can fire up eM Client and it will run, however, once it is running successfully, you will want to quit the app and then configure it in CrossOver to "Run in Desktop Mode", as it tends to hang if you minimize it's window in any way and then bring it back to regular size (this does not seem to occur once set to run in desktop mode). One caveat that you may run across is that in order to properly set up some email accounts, you may need to turn off your WiFi on your Chromebook until you have ALL of the settings correct for your email account (I had to do this with GMail in order to get the ports set correctly). The only other caveat I have run across is that if you have a LOT of emails (I have over 25,000 in one of my boxes) the sync will periodically hang. I have not yet been able to determine the cause, but if I force close eM Client, and start it back up again, it will go through its diagnostics and continue the syncing of emails. I had to repeat this process multiple times to get all 25,000 emails synced. However, once they were synced, the app seems to run just fine.
UPDATE 10-18-18
It appears that the cause of it hanging is the size of the actual emails (thus attachments usually, but sometimes just photos in the email). If you keep the size to around 5MB max., it seems to not hang. I went through all of my emails and deleted large attachments and syncing only seemed to hang when it would hit the few I missed that were larger than about 5MB.