As you know, when sending a message using Exchange or Exchange Online, there is a timeout when the system is not able to deliver the message before sender receive the Non Delivery Report (NDR).
This timeout is to 24 hours by default and it was not possible to change it; well, until now.
You can now manage this expiration timeout – within a 12 hours to 24 hours window.
To do so, you need to have the Exchange Online PowerShell module (https://www.powershellgallery.com/packages/ExchangeOnlineManagement/).
Once connected using the Connect-Exchange Online command you can check if this option is available in your tenant using the command
Get-TransportConfig | fl *messageexpiration*
If you see the MessageExpiration setting, then you can configure it using the command
Set-TransportConfig –MessageExpiration 12:00:00
NOTE this example sets the expiration to 12 hours; you can define any value between 12 hours to 24 hours using the format dd:hh:mm:ss (14:30:00 for 14h30 expiration)