To ensure proper handshaking and validation with SMTP servers to verify emails, please make sure your email address that you entered here adheres to the following standards:

1. SPF (Sender Policy Framework): Ensure that your domain has a valid SPF record set up. SPF helps prevent email spoofing by specifying which mail servers are authorized to send emails on behalf of your domain.
2. DKIM (DomainKeys Identified Mail): Set up DKIM for your domain. DKIM adds a digital signature to outgoing emails, allowing the receiving server to verify the authenticity of the sender and the integrity of the email's content.
3. DMARC (Domain-based Message Authentication, Reporting, and Conformance): Implement a DMARC policy for your domain. DMARC builds upon SPF and DKIM, providing an extra layer of protection and specifying what actions to take if an email fails authentication checks.

By complying with these standards, your validation will have a higher chance of successful results and lower the risk of ending up in invalid values. Please click this article for more details.