Hello,

To prevent negative influence on the system performance and ensure fast delivery for all users, the limit of single message has been balanced to 25 MB.

This limit applies to all messages (inbound, outbound and internal) and currently, it's not a configurable parameter to increase the limit.

Appreciate if you could provide your feedback regarding your requirement, which will help Microsoft to improve Office 365 product and build mutual relationship with customers.

Thanks,
Lester Zhang