Open the Exchange Management Shell to view the global default attachment size is 10MB
Get-TransportConfig | Format-List MaxReceiveSize,MaxSendSize,MaxRecipientEnvelopeLimit
Set organizations limit (default value: 10MB) in the mail stream
Amended to 25MB attachment size
You need to restart the Microsoft Exchange Information Store service to take effect
Since the transmitting and receiving connector connected to a default size limit for attachments 36MB 36MB globally valid maximum size of attachments, if more than 36MB, but also you need to change the transmitting and receiving connector connected default attachment size limit