Why are emails going to the spam folder
The real causes of junked mail, ordered by how often they turn out to be the problem, each with the fix and a way to prove it from a message you actually received.
Deliverability
Why the mail your app sends lands in spam, bounces or never arrives: SPF, DKIM and DMARC, sender reputation, and how sites detect and block disposable addresses.
Powered by the Email Testing APIHow websites detect temporary email, and how to build that check
Three cheap signals do almost all the work: a public domain blocklist, what DNS says the domain can receive, and how the signup behaves. Here is how to implement each one and test it.
SPF, DKIM and DMARC, explained by what a receiver actually does
Three DNS records, one verdict. What each one proves, the order a receiving server applies them, and why a message can pass SPF and still fail DMARC.