The Email Activity Services module in OfficeRnD Flex has a Resend Email button. This button can be used when an email can't be sent or delivered due to technical failures or suppression events.
The Resend Email button is visible in the top-right corner when you click on a thread to open it in Email History View:
When can I resend an email?
After sending the original message, the Resend Email button can be used for three days (or more, depending on the domain configuration in Mailgun). After the time limit expires, the button will no longer be available.
How to resend an email
Go to Collaboration > Email Activity.
Find the email you want to resend and click View Details.
Click Resend Email.
In the Resend Email dialog, review the recipient name, date sent, and status of the email you are about to resend.
Click Resend Email.
When the email is successfully resent, a success message will be shown, and a new record will be added to the Email Activity Service page with the status Resent: