I’ve been an eM Client free user since 2018. There was something about a demo version that has expired. Now I can no longer send or receive e-mail. Website stated it would send activation key, but since I can no loger receive e-mails, I haven’t seen it.
Login to your email “via your webmail online in a browser” and you should have the key in your Inbox or otherwise “check your spam / junk folder” incase your mailbox possibly detected it has spam.
Now if you can’t find it anywhere in your mailbox online, then go to the following webpage and type in your email address you registered with, and the licence key will be resent to you.
Then copy the key from your webmail, and go in eM Client to “Menu / Help / Licence / Activate”.