One of the best resources is the blog Word to the Wise. Also, Return Path is a service that enhances deliverability and they publish a lot of great information through their blog and white papers. Below is are some best practices from the major ESPs.
Where can I learn more about Deliverability and Email?
Where can I learn more about Deliverability and Email?
Other helpful resources
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Mail Tester
Spam-check your emails before they send -
Postbin
Debug webhooks easily -
SenderScore
Check IP reputation -
MXToolbox
Troubleshoot DNS issues