Here are a few things you can do to improve the delivery of your emails to some of the major email providers:

1. Review your email practices and ensure that you are following best practices for sending outbound emails.
• Ensure that you have consent to send emails to the recipients.
• Send only emails to those who have requested them.
• Ensure your emails are compliant with CAN-SPAM acts.
• Include a one-click unsubscribe option in each email.
2. Implement email authentication protocols such as DKIM and SPF to prove the identity of your sender domain.
3. Monitor the delivery rates of various email providers and troubleshoot any sources of blocking or filtering.
4. Analyze the servers used to send outbound emails to ensure a consistent IP reputation.