Unable to send message with Attachment even though Proper Message size limits 15 MB has been set on Receive, Send and at Transport Level which also includes MIME overhead of 37% still not able to send/receive message

Exchange 2010, Unable to send message with Attachment even though Proper Message size limits 15 MB has been set on Receive, Send and at Transport Level which also includes MIME overhead of 37% still not able to send/receive message.

then try this command 

Set-TransportConfig -ExternalDsnMaxMessageAttachSize 15MB -InternalDsnMaxMessageAttachSize 15MB

In Exchange 2013
New-SystemMessage is a command used to set the DSN (Delivery status Notification)

for reference
https://technet.microsoft.com/en-us/library/aa998878%28v=exchg.150%29.aspx



some Additional Knowledge and default Series for configuring limit is

• Organizational Level # Is the Highest level in an organization
• Send Connector
• Receive Connector
• AD Site Links
• Routing Group Connectors
• Mailbox Level      # Is the lowest level and take precedence over all the settings

Shell Commands where Message Limit can be checked

Get-ForeignConnector | fl Name,MaxMessageSize
Get-SendConnector | fl Name,MaxMessageSize
Get-ReceiveConnector | fl Name,MaxMessageSize
Get-ADSiteLink | fl Name,MaxMessageSize
Get-RoutingGroupConnector | fl Name,MaxMessageSize
Get-TransportConfig | fl MaxSendSize,MaxReceiveSize
Get-DistributionGroup | fl name,MaxSendSize,MaxReceiveSize
Get-DynamicDistributionGroup | fl name,MaxSendSize,MaxReceiveSize
Get-Mailbox | fl name,MaxSendSize,MaxReceiveSize
Get-MailContact | fl name,MaxSendSize,MaxReceiveSize
Get-MailPublicFolder | fl name,MaxSendSize,MaxReceiveSize
Get-MailUser | fl name,MaxSendSize,MaxReceiveSize

Get-Mailbox -FIlter {MaxSendSize -ne $null -OR MaxReceiveSize -ne $null} | ft Name,MaxSendSize,MaxReceiveSize