The first one is that you must adequately configure DKIM, SPF, and DMARC records for your sender domain instead of verifying the sender’s email address for better email deliverability. For this, you can follow this guide.
The second one is the introduction of easy one-click unsubscribe button on the email header. MailBluster has also implemented an easy one-click unsubscribe header automatically to all outgoing emails to make it easier for recipients to unsubscribe, reducing the spam complaints, as shown below :
The third one is Mailbox providers will require that all senders keep spam complaint rates below 0.3% to avoid having their email treated as spam by the mailbox provider. It is recommended to enroll with Google Postmaster Tools to monitor their spam complaint rates for Gmail recipients.
Kindly be informed that disregarding these requirements could result in Gmail and Yahoo rejecting the delivery of emails to their intended recipients.