Hello Boss,
I've been working lately as a Google Apps Script developer in a US-based company specializing in Lead generation. I've developed a tool in GAS and Google Sheets that uses Gmail API for Automated Bulk Email Sending daily with analytics features for monitoring Bounced and Positive response leads, also I tried many APIs and SMTP before getting into GAS like Mailgun, Mailtrap, Brevo, Mailchimp, etc.
Let's have a quick chat to discuss this further