Timothy Jacobs

WP Mail Debugger captures and displays all emails sent through wp_mail() for debugging and troubleshooting. A new admin menu, WP Mail Debugger, is added under the Tools menu.
Get the <a href="https://apps.apple.com/us/app/wp-mail-debugger/id1547093438?mt=12" rel="nofollow ugc">Mac App</a> to connect to multiple WordPress websites from one convenient location.

WP Mail Debugger

I "found" this plugin when its creator presented it at WCPhx 2020. Its extremely easy to use, and is helpful in a day and age when SPFF and DKIM issues make debugging mail tough. Show your users the mail is going out. Or as a plugin developer, use it to review output.

This is so good

WP Mail Debugger captures and displays all emails sent through wp_mail() for debugging and troubleshooting.

nikita.global

Create your own notification bot which will send emails to your dashboard users via telegram.
Sends all mails to telegram user via your own bot. 
No need in many other plugins as you can use any email notifications which will be redirected to telegram
<a href="https://nikita.global" rel="nofollow ugc">https://nikita.global/</a>
Your website should support https.
** Message Filters ** 
Currently can send mails as plaintext, files, subjects only and truncated message. 
You can extend this range using the filters – see source code.
This plugin makes HTTP-requests to 3rd party service <a href="https://core.telegram.org/api" rel="nofollow ugc">Telegram API</a> 
to send notifications.

NG-Mail2Telegram

very good!

Create your own notification bot which will send emails to your dashboard users via telegram.

WP Mail Debugger vs NG-Mail2Telegram