If you are doing this from the Contact object, it should be straight forward, just create a new Action to send an Email. If you are doing this from another object like Account, Opportunity, etc... make sure you have a lookup field to Contact (or any other object in which you have a field of Email Data Type) and populate it with the desired Contact
- Create a new Action for the object which you are trying to send the email from. In the example below I created a new Action for the Account (after I had the lookup created for the Contact, which I called Primary Contact)
- After the Action is created, create a new "Predefined Field Value" and select the "To" field.
- Navigate through your objects/relationships and select the Email field
- Modify the page layout to add the new Action
After that, if you have the lookup field populated, it should automatically set the default value for the "To" field.
Please look at the images below:
Let me know if you have further questions, as well if you were able to get it to work :)