Hello Dane, you can use a custom spell check dictionary while working with eM Client. I’m not completely sure what formatting can you export your custom dictionary in, but eM Client uses a local dictionary for your regular spell check and a custom library for “your words”. By selecting an underline word in eM Client and right clicking the word, you can add it to dictionary.
This will create a dictionary file in your eM Client installation folder under “Dictionaries”, you can open the custom dictionary and add the custom word from your outlook dictionary, each on a new line in order to use these with eM Client.
Hope this helps,