Ability to view message in Log entries
Add an HTML view of the sent message to Log entries. This would allow administrators (and other stakeholders, when multiple user support becomes available) to review messages as they were sent as needed.
This is a common task for my clients on Postmark to perform and Postmark gives them a view to do this. Similar to Mailgun, Postmark retains only the last 45 days of entries (Mailgun is 30). These time ranges are sufficient for responding to most inquiries that administrators and support staff receive as to who received (or didn't receive) what message when and what did it look like.

Hello,
This week, we released new improvements to our logs page. You can now see the rendered HTML view when you go to the “view details” tab of the message.
Messages can be shown for a total of 3 days after they’ve been sent via Mailgun.
Josh
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Ho Kuen Leung (PikachuEXE) commented
Thanks for implementing that
But it seems the display of non-ASCII characters are broken?
We hope this can be fixed soon -
Lahav Gan commented
When using 'show message' in the log, it would be great to get a button and show the HTML msg rendered as the user would see it...
I've used send-in-blue service in the past, and it has that feature