I added an incorrectly spelled word to the spell checker dictionary. How do I edit my additions?
Go to where your eM Client mail folders are stored, usually in the “C:\Users\YourComputerAccountName\AppData\Roaming\eM Client Preview” (or the equivalent) on Windows. In that folder look for file named “en-US.custdic”. You can open that file with any plain text editor and delete the incorrectly enter entry. Just be sure to save the file with the exact same name.
NOTE: eM Client’s backup function does not seem to capture the custom dictionary, so make sure to back it up manually from time to time, too.