https://docs.microsoft.com/en-us/Exchange/architecture/client-access/client-message-size-limits?view=exchserver-2019
%windir%\system32\inetsrv\appcmd.exe set config "Default Web Site/Microsoft-Server-ActiveSync/" -section:system.webServer/security/requestFiltering /requestLimits.maxAllowedContentLength:30000000
%windir%\system32\inetsrv\appcmd.exe set config "Default Web Site/Microsoft-Server-ActiveSync/" -section:system.web/httpRuntime /maxRequestLength:10240
%windir%\system32\inetsrv\appcmd.exe set config "Exchange Back End/Microsoft-Server-ActiveSync/" -section:system.webServer/security/requestFiltering /requestLimits.maxAllowedContentLength:30000000
%windir%\system32\inetsrv\appcmd.exe set config "Exchange Back End/Microsoft-Server-ActiveSync/" -section:system.web/httpRuntime /maxRequestLength:10240
%windir%\system32\inetsrv\appcmd.exe set config "Exchange Back End/Microsoft-Server-ActiveSync/" -section:appSettings /[key='MaxDocumentDataSize'].value:10240000