Restricting mail routing based on message size

You can set size limits on messages to prevent large messages from consuming network bandwidth. There are two types of message size limits: a maximum message size and a low-priority size range. Messages that exceed the maximum message size are returned to the sender as undeliverable. Messages that are smaller than the maximum size, but that fall within the specified size range, are marked low-priority and routed during off-peak hours (12 AM to 6 AM by default).

About this task

Domino® uses the maximum message size you specify as the upper limit of the low-priority size range. Before specifying a low-priority size range, you must set a maximum message size.

The size restrictions you set in the Configuration Settings document apply to every message the Router handles, regardless of whether the message is inbound or outbound, routed over Notes® routing or over SMTP. To set a unique size limit on some part of your messaging traffic, you must set up distinct routing paths for that traffic and then create separate Configuration Settings documents for servers on those paths. For example, if you want to place a 500KB limit on inbound SMTP mail and a 1000KB size limit on internal mail, create two Configuration Settings documents: one for the servers that receive mail from the Internet that specifies a 500KB size limit and a second for your internal mail servers that specifies a 1000KB limit.

When setting size restrictions, keep the following in mind:
  • Total message size is equal to the sum of the message text and the size of all attachments.
  • You can change the default hours for routing low-priority mail.
  • You can customize the text of delivery failure messages.
  • On Domino® SMTP servers you can use the ESMTP SIZE extension to prevent inbound transfer of messages that exceed the specified maximum message size. You can also use the outbound ESMTP SIZE extension to configure Domino® to honor size restrictions on a target server when transferring outbound SMTP mail.
    Note: SMTP transfer-encoded sizes of messages are larger than the Notes® size of a message. For example, a message with a binary attachment that is base64-encoded is approximately 25% larger on transfer, and this larger size will be used in maximum size calculation.


  1. Make sure you already have a Configuration Settings document for the server(s) to be configured.
  2. From the Domino® Administrator, click the Configuration tab and expand the Messaging section.
  3. Click Configurations.
  4. Select the Configuration Settings document for the mail server or servers you want to administer, and click Edit Configuration.
  5. Click the Router/SMTP > Restrictions and Controls > Restrictions tab.
  6. Complete these fields in the Router Restrictions section, and then click Save & Close:
    Table 1. Router Restrictions fields



    Maximum message size

    The maximum message size in KB (thousands of bytes) the server accepts. The Router rejects any messages that exceed this size for both transfer and delivery. The default is 0 KB, which does not limit message size.

    Send all messages as low-priority if message size is between

    Choose one:

    • Enabled
    • Disabled (default)

    If you choose Enabled, specify the lower limit of the size range in KB. By default the lower limit is 50KB. The upper limit of the size range is defined in the field Maximum message size. When enabled, messages with a size between the value entered in this field and the value in the Maximum message size field are sent as low-priority messages.

  7. The change takes effect after the next Router configuration update. To put the new setting into effect immediately, reload the routing configuration.