As far as the default functionality concerned. All you have to do is follow the steps described below and you'll have your custom button linked with the default Salesforce email author.
- Create a custom button.
- Add the custom button on your page layout.
- Edit the custom button and type in a URL with your custom parameters.
Create a custom button
You can create custom button by going under
and edit your object. Scroll down to the following section and press New Button or Link button. Give label, name and description to your button and Save.
Add custom button on Page Layout
To add custom button on your page layout scroll to the page layouts section and Edit the page layout on which you want to add this button.
Then just drag & drop the button on the Custom buttons section and save the layout.
Edit the custom button Now this time you have to scroll to the Buttons, Links, and Actions section and edit your custom button.
Once in this section here are the following things you need to focus on.
- URL of Email Author
- Parameters list
URL of Email Author Following is the base URL of email author you need to point on.
If you simply put this piece of URL in front of your org's base address like this you'll get a pretty email author opened and all it is waiting is your input and the time you'll hit the Send button.
Apparently by your question this is all you need. But if you need to pre fill some of the information and also have an email template that you want to pull your email content from then you need to consider the following parameters list and add them into the mix. You can get the guidance from the attached screenshot of Edit button. And for your reference I'll add the complete URL at the bottom of this answer which is actually customized according to my needs and for my org.
Parameters list Below is the map of parameter name to parameter value.
p2_lkid To (can be Contact or Lead Id)
p3_lkid *Related To (usually the parent record Id)
p23 Email Body
p24 Additional To
Template_Id Salesforce email template Id
retURL *Redirection page when cancel button is clicked
Complete URL for your reference
I hope it will help you and for any further questions you're welcome to ask under comments. Thanks.