How To Retrieve or Set Maximum Send/Receive Size For Mail Contacts

Set the maximum message size for a specific mail contact or group of mail contacts

Get-MailContact -resultsize unlimited | where {$_.externalemailaddress -like "SMTP:CAN????@stores.pvt"} | Set-MailContact -MaxReceiveSize 65KB -MaxSendSize 65KB -ForceUpgrade

Retrieve specific mail contacts and report on their maximum send and receive message size 

Get-MailContact -resultsize unlimited | where {$_.externalemailaddress -like "SMTP:CAN????@stores.pvt"} | ft name, externalemailaddress, maxsendsize, maxreceivesize