What is important in e-mail testing - 10 points:
1. Use good/warm IP's for send-out
2. THE click works in all clients/mobiles
3. Visual overview from many clients
4. Monitor clickrates / openrate
5. Monitor delivery status codes, user agents, 4xx, 5xx, 2xx
6. Good looking and understandable without pictures, alt tag, contrast of text, font, default: not loaded in many clients
7. Size kbyte + length/ clipped / cut off / included code to load - e.g font !?
8. DNS, server stuff, DKMI, SPF, DMARC - allowed servers to send from ...
9. Use the advantage of an extra preheader
10. Clean your recipient list! If no clicks/open or if 5xx state pause the send-out!
11. Monitor reply to address - don't be arrogant with do_not_reply@ - you chose to communicate via e-mail so be prepared for responses!
12. html syntax checker / linter
13. unsubscribe possibility