is mobile-friendly
is free from "spammy" words
is relevant/helpful for the reader
has a decent image/text ratio (or no images)
and easily shows the reader where to unsubscribe
📈 Reputation
Just like a credit score, you have an email reputation to maintain as well
Factors that affect it your reputation include—
bounces
blacklists
open rates
reply rates
IP reputation
spam complaints
domain reputation
and consistent sending behavior
⚙️ Infrastructure
You'll want to keep an eye on a few things when choosing a quality email service provider (ESP)
Do they have—
support for proper DNS setup
clean and responsive email code
protocols for high-volume senders
options to use shared vs. dedicated IPs
🔒 Authentication
This can get super technical, so I recommend researching these 3 concepts to learn more about them: DKIM, SPF, and DMARC
Here's a podcast episode from @ConvertKit that goes into more detail