How to Customize the Exchange Online Message Expiration Timeout Interval
Microsoft is deploying a change to the Exchange Online transport server to allow tenants to set the message expiration timeout interval to between 12 and 24 hours. The default for the service remains at 24 hours. Reducing the interval means that users will learn about message failures sooner. The hope is that they’ll be able to respond to those failures and resend messages once they learn about problems.