Hello, thank you very much for inviting me for your project. I am an experienced, certified Salesforce developer and currently working as technical lead of a enterprise salesforce application for an MNC. I have implemented a number of projects in this freelancer which connects with Quickbook, Xero, ActiveCampaign and many custom API from salesforce. I have specifically worked on scheduler and batch for number of projects with API integration and well aware of test classes, limits and best practices. You are welcome to go through my projects in freelance. I am very well aware of the Salesforce apex callout and trigger mechanism with the industry best practice. The trigger that you require can be built which will issue apex callout from a separate apex class to [login to view URL] API. Your specifications are very clear however I have just couple of questions to clarify. In 2.3 - you mentioned "custom setup type". Could you please clarify are you trying to say custom object or custom settings entry? Also where the two custom fields "Correo_Electronico_Valido__c" and "Correo_Electronico_Revisado__c" will be that need to be updated after the scheduler runs. If I am trustworthy, then please let me know. We can discuss those points and the implementation can be completed within max 4-5 days (contains over 90% test coverage). Thanks for your time.
UPDATE - Hello, Please have a look at this recording. I have already implemented first draft of the trigger and singleEmail call verification with Neverbounce. In the recording I have shown that with update of a lead the neverbounce api is called with oAuth authentication and the api endpoint is called to verify the email address of the lead. Hope you like my work. Here is the link - [login to view URL]