Hello,
We come from the Postbox world… We are new users of eM Client.
With Postbox there was the integration of Connectix Antidote. It is a spelling and grammar corrector. It is very usefull for french users.
I asked the editor of Antidote, and they told me to express my desire that eM Client open’s up itself to this connector Connectix to be able to use Antidote.
So, here it is : I am expressing my desire to see eM Client being compatible with Antidote like Postbox was 
Andrew