You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser. The stock Mail Apple Watch app, displays tiny text, which is practically unusable.
Download Outlook, and sign into all of the email accounts that you use.
Add it as a complication, and when you receive an email, use that, instead of the stock app.
Text is much larger, and visible, and you can reply/delete etc as required.
Hope this helps some of you.
Wishing you well.
Tommy