Limiting Attachment Size for Email Delivered and Received

In order to limit attachment size for incoming emails these steps can be followed,
1- Determine existing situation by using “GET” command on Exchange Management Shell
[PS] C:\Windows\System32>Get-TransportConfigClearCategories : True
DSNConversionMode : UseExchangeDSNs
GenerateCopyOfDSNFor : {5.4.8, 5.4.6, 5.4.4, 5.2.4, 5.2.0, 5.1.4}
InternalSMTPServers : {}
JournalingReportNdrTo : <>
MaxDumpsterSizePerStorageGroup : 18MB
MaxDumpsterTime : 7.00:00:00
MaxReceiveSize : unlimited
MaxRecipientEnvelopeLimit : unlimitedMaxSendSize : 10MBTLSReceiveDomainSecureList : {}
TLSSendDomainSecureList : {}
VerifySecureSubmitEnabled : False
VoicemailJournalingEnabled : True
WritingBrandingInDSNEnabled : True
Xexch50Enabled : True

Max Send Size portion shows that maximum limit is 10 MB,

2- Now we can use “SET” command to alter the value

[PS] C:\Windows\System32>Set-TransportConfig -MaxSendSize:307203- For reconfirmation again check values by “GET” command

[PS] C:\Windows\System32>Get-TransportConfigClearCategories : True
DSNConversionMode : UseExchangeDSNs
GenerateCopyOfDSNFor : {5.4.8, 5.4.6, 5.4.4, 5.2.4, 5.2.0, 5.1.4}
InternalSMTPServers : {}
JournalingReportNdrTo : <>
MaxDumpsterSizePerStorageGroup : 18MB
MaxDumpsterTime : 7.00:00:00
MaxReceiveSize : unlimited
MaxRecipientEnvelopeLimit : unlimited
MaxSendSize : 30MB
TLSReceiveDomainSecureList : {}
TLSSendDomainSecureList : {}
VerifySecureSubmitEnabled : False
VoicemailJournalingEnabled : True
WritingBrandingInDSNEnabled : True
Xexch50Enabled : True

Note: 
Same steps can be followed to change MaxReceiveSize however if you are using EDGE server roles, the change must be done on all HUB and EDGE servers.