Resending of failed Emails
Can configure the resending time periods
The whole mailbox will be checked once a day by default
If there are any failed emails, it will resend
Automatic checking for resending the failed emails can be configured once a day or once a week, or once an Hour etc
By default, the whole Emails will be checked once a day
If there are any failed emails, then it will resend
To change the time period
Activate the developer mode,Then Settings->Technical->Automation->Scheduled Action
Open the record named 'Auto Resend Emails'
Configure it here