There are several places to look when configuring the maximum permitted Email Message Sizes within your organisation. A maximum receiving message size of 10–15MB should be a realistic figure. Anything larger and it is likely that the ISP will block the message anyway. Some organisations block attachments over 2MB anyway. Therefore, it is worth setting a maximum sending message size to avoid excessively large messages being returned to your users by the recipient’s server. If you are using a POP3 Connector, it could be argued that enforcing receiving message sizes is pointless – as the message will have to be downloaded before it can be rejected (assuming you want to send an NDR). However, setting this restriction will prevent users mailboxes from becoming full as a result of abnormally large messages.
 Within Exchange System Manager
Exchange System Manager -> Global Settings -> Message Delivery -> Properties -> Defaults.
 Within the SMTP Connector Properties
Specify a maximum message size within “Allowed Sizes”.
Routing Groups -> Connectors -> Small Business SMTP Connector
 Within the SMTP Virtual Server
Servers -> Protocols -> SMTP -> SMTP Virtual Server -> Properties -> Messages
 On Per User Basis within “Active Directory Users and Computers”.
NDR Reports Created by Exchange 2000
The NDR Report generated by Exchange 2000 will have the subject: “Delivery Status Notification (Failure)”. Note that the user is not advised that the message was “too big”. If the message has been “rejected” by a third party (ISP), the subject header may well be different. Additionally, if there is any Mail Filtering software installed on the server, this could also be the source of the NDR.
NDR Message Sizes
If the Maximum Sending Message Size on the server is less then the Maximum Receiving message size, this may result in the NDR being blocked (by your own server before it leaves your organisation). To avoid this, refer to the following Microsoft Knowledge Base Article: Q308303 Strip Attachments for Messages That Generate an NDR.
Maximum Mailbox Sizes
The size of each users mailbox can be restricted as follows:
Servers -> System Policies -> Mailbox Store Limits -> Properties
GFI Mail Essentials POP3 Connector
Assuming SMTP is not in use, GFI Mail Essentials provides a facility for limiting the size of messages downloaded from a POP3 Server.
Mail Essentials Configuration -> POP2Exchange -> General -> Properties -> “Do Not Download Messages Larger Than”
© Stephen Holder
June 22, 2005