Use Process Builder!
Let’s create a new Process to verify the email address of a Lead as soon as it is created. Switch to Process Builder by Navigating to Salesforce setup | Quick Find | Process Builder.
1. Create a new Process.

2. Choose the object on which the process builder needs to be implemented Here, Lead is the object.
Note: Select the option ‘When a Record is created’.

3. Set the criteria according to your requirement. Here for eg,
Field: Email
Operator: is Null
Type: Boolean
Value: False

4. Now, in the immediate action:
- Select Action Type: Apex
- Specify an Action name, Here: ‘Verify Email Address’.
- Select the Apex class ‘Verify Email From Process Builder’.
- Set Apex Variable as:
- Field: Email API
a. Field: Email API
Type: String
Value: SuppliedEmail
b. Field: Record ID
Type: Field Reference
Value: [Lead].Id
Here, supplied email is the API name of the field which consists of the email address.
[Lead].Id is the Id of the Record on which the email address is saved.

5. Click on save.