If you've updated or changed the message content in a Send Email Action and aren't seeing the changes reflected when you send yourself a test message, make sure you have updated both the HTML Message Body and Plain-Text Message Body versions of the message.
If the emails received are not reflecting your most recent edits, the most likely cause is that the edits were made to the Plain-Text version of the email and not also included in the HTML version.
When you initially create or edit the message, you will only be editing the HTML Message Body. The Plain-Text version will be automatically updated based on changes to the HTML version.
However, if you have elected to disable the Automatically generate plain-text version setting, you will be editing both the HTML and Plain-Text versions independently.
Note: Most email recipients will be receiving the HTML version of your email, though if the recipients have disabled HTML email within their email client, they will see the Plain-Text version.
If you need to edit your Plain-Text version independently of the HTML version, de-select the Automatically generate plain-text version.
Make all your changes, double-check that they match (if you need them to) and Save Action. Test it again and your changes should be reflected in the new message you receive.