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Managing Message Size Limits

 

Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007

Topic Last Modified: 2009-07-14

This topic describes the message size limits that you can apply to individual messages that traverse the Microsoft Exchange Server 2007 organization. You can restrict the total size of a message or the size of the individual components of a message, such as the message header, the message attachments, and the number of recipients. You can apply limits globally for the whole Exchange 2007 organization, or specifically for a particular connector or user object.

As you plan the message size limits for your Exchange 2007 organization, consider the following questions:

  • What size limits should I impose on all incoming messages?
  • What size limits should I impose on all outgoing messages?
  • Does my Exchange 2007 organization have a mailbox quota?
  • How do the message size limits that I have chosen relate to the mailbox quota size?
  • Are there special users in my Exchange 2007 organization who must send or receive messages that are larger that the specified allowed size?
  • Does my Exchange 2007 network topology include other messaging systems or distinctly separate business units that have different message size limits?

The size limits that are available for individual messages can be divided into the following basic categories:

  • Message header size limits   These limits apply to the total size of all message header fields that are present in a message. The size of the message body or attachments is not considered. Because the header fields are plain text, the size of the header is determined by the number of characters in each header field, and by the total number of header fields. Each character of text consumes 1 byte.
    noteNote:
    Some third-party firewalls or proxy servers apply their own message header size limits. These third-party firewalls or proxy servers may have difficulty processing messages that contain attachment file names that are greater than 50 characters, or attachment file names that contain non-US-ASCII characters.
  • Message size limits   These limits apply to the total size of a message. This includes the message header, the message body, and any attachments. Message size limits may be imposed on incoming messages or outgoing messages. For internal message flow, Exchange 2007 uses the custom X-MS-Exchange-Organization-OriginalSize: message header to record the original message size of the message as it enters the Exchange 2007 organization. Whenever the message is checked against the specified message size limits, the lower value of the current message size or the original message size header is used. The size of the message can change because of content conversion, encoding, and agent processing.
  • Attachment size limits   These limits apply to the maximum allowed size of a single attachment within a message. The message may contain many attachments that greatly increase the overall size of the message. However, an attachment size limit would apply to the size of an individual attachment only.
  • Recipient limits   These limits apply to the total number of message recipients. When a message is first composed, the recipients exist in the To:, Cc:, and Bcc: header fields. When the message is submitted for delivery, the message recipients are converted into RCPT TO: entries in the message envelope. A distribution group is counted as a single recipient during message submission.

The scope of the limits that are available for individual messages can be divided into the following basic categories:

  • Organizational limits   These limits apply to all Exchange 2007 servers that exist in the organization. The specified message limits apply to all Exchange 2007 servers that have the Hub Transport server role installed. On an Edge Transport server, the specified limits apply to the specific server.
  • Global limits   These limits apply to all Exchange 2007 and Exchange Server 2003 servers that exist in the organization. The global message limits are stored in the Active Directory directory service.
    In the release to manufacturing (RTM) version of Microsoft Exchange Server 2007, it is common for the organization limits and the global limits to conflict. When the organizational limits and the global message limits conflict, the lowest value takes precedence. In Exchange 2007 RTM, you must use Exchange System Manager on an Exchange 2003 server or the Active Directory Service Interfaces (ADSI) Edit tool to modify global message limits. For more information, see How to Modify Exchange 2003 Global Message Size Limits in Exchange 2007 RTM.
    In Microsoft Exchange Server 2007 Service Pack 1 (SP1), the condition that cause the organization limits and the global limits to conflict has been eliminated. Changes that you make to the organizational limits are automatically copied to the corresponding global limits. In Exchange 2007 SP1, you can modify the organizational limits by using the Set-TransportConfig cmdlet in the Exchange Management Shell, or by configuring the Hub Transport server organization configuration properties in the Exchange Management Console.
  • Connector limits   These limits apply to any messages that use the specified Send connector, Receive connector, or Foreign connector for message delivery. Connectors are defined on Hub Transport servers or Edge Transport servers.
    In Exchange 2007 SP1, you can also set message size limits on the following types of connections:
    • Active Directory site links   Hub Transport servers use Active Directory sites and the costs that are assigned to the Active Directory IP site links to determine the least cost routing path from each Hub Transport server in the organization to every other Hub Transport server in the organization. You can use the Set-AdSiteLink cmdlet to assign an Exchange-specific cost to the Active Directory IP site link. The Exchange-specific cost is a separate attribute that is used instead of the Active Directory-assigned cost to determine the least cost routing path. Any message size limits that are specified on an Active Directory site link don't affect the selection of the least cost routing path. Any messages that exceed the maximum message size limit on any Active Directory site link included in the least cost routing path won't be delivered, and will generate a delivery status notification (DSN) that has the value 5.3.4. For more information, about message routing in Exchange 2007, see Planning to Use Active Directory Sites for Routing Mail.
    • Routing group connectors   A routing group connector is used to send and receive messages between Exchange 2007 Hub Transport servers and Exchange 2003 or Exchange 2000 bridgehead servers when the organization is running more than one version of Exchange Server. Any message size limits that are specified on a routing group connector don't affect the selection of the least cost routing path. Any messages that exceed the maximum message size limit on any routing group connector in the least cost routing path won't be delivered. They will generate a DSN that has the value 5.3.4. For more information about routing group connectors, see Message Routing in a Coexistence Environment.
    For more information about message size limits on Active Directory site links and routing group connectors in Exchange 2007 SP1, see How to Configure Message Size Limits for Internal Routing.
  • Server limits   These limits apply to a specific Hub Transport server or Edge Transport server. The specified message limits are not stored in the Active Directory directory service. You can set the specified message limits independently on each Hub Transport server or Edge Transport server.
    Message size limits can apply to Microsoft Office Outlook Web Access on a Client Access server. For more information, see How to Manage Maximum Message Size in Outlook Web Access.
  • User limits   These limits apply to a specific user object, such as a mailbox, contact, distribution group, or public folder.

The following table shows the organizational limits.

Organizational limits

Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Set-TransportConfig

MaxReceiveSize

Unlimited

10 MB

Set-TransportConfig

MaxSendSize

Unlimited

10 MB

Set-TransportConfig

MaxRecipientEnvelopeLimit

Unlimited

5000

Transport rule on a Hub Transport server that applies to all Hub Transport servers in the organization.

AttachmentSizeOver

Not configured

Not configured

The following table shows the global limits.

Global limits

Source Property Default value

Active Directory

  • delivContLength in Active Directory
  • Incoming message size in Exchange System Manager Global Settings in Exchange 2003

10240 KB (10 MB)

Active Directory

  • submissionContLength in Active Directory
  • Outgoing message size in Exchange System Manager Global Settings in Exchange 2003

10240 KB (10 MB)

Active Directory

  • msExchRecipLimit in Active Directory
  • Maximum number of recipients in Exchange System Manager Global Settings in Exchange 2003

5000

In Exchange 2007 RTM, the initial values of the global limits differ from the default values only when the organization was upgraded from Exchange 2003, and a numeric value was specified for Incoming message size, Outgoing message size, or Maximum number of recipients. The numeric value is preserved after the upgrade to Exchange 2007 RTM.

In Exchange 2007 RTM, any changes that you make to an organizational limit by using the Set-TransportConfig cmdlet are never copied to the corresponding global limit. In Exchange 2007 RTM, you must use Exchange System Manager on an Exchange 2003 server or the ADSI Edit tool to modify global message limits. For more information, see How to Modify Exchange 2003 Global Message Size Limits in Exchange 2007 RTM. We recommend that you set the global limits and the corresponding organization limits to the same values.

The following list describes the conditions that cause the initial values of the global limits to differ from the default values in Exchange 2007 SP1:

  • The existing numeric values of delivContLength, submissionContLength, or msExchRecipLimit are preserved for the following circumstances:
    • The organization was upgraded from Exchange 2007 RTM and the corresponding organizational limit values that are specified by the MaxReceiveSize parameter, the MaxSendSize parameter, or the MaxRecipientEnvelopeLimit parameter on the Set-TransportConfig cmdlet were set to Unlimited.
    • The organization was upgraded from Exchange 2003, and a numeric value was specified for Incoming message size, Outgoing message size, or Maximum number of recipients.
  • The values of delivContLength, submissionContLength, or msExchRecipLimit are changed to match the values of the corresponding organizational limits that are specified by the MaxReceiveSize parameter, the MaxSendSize parameter, or the MaxRecipientEnvelopeLimit parameter on the Set-TransportConfig cmdlet when all the following conditions are true:
    1. The organization was upgraded from Exchange 2007 RTM to Exchange 2007 SP1.
    2. A numeric value was specified for delivContLength, submissionContLength, or msExchRecipLimit.
    3. A different numeric value was specified for the corresponding organizational limit in the MaxReceiveSize parameter, the MaxSendSize parameter, or the MaxRecipientEnvelopeLimit parameter.

In Exchange 2007 SP1, you shouldn't modify the global limits directly. In Exchange 2007 SP1, if you set a global limit to a different value than the corresponding organizational limit, you will generate event log errors. When you want to modify the organizational limits or the global limits in Exchange 2007 SP1, you should use the Set-TransportConfig cmdlet in the Exchange Management Shell or the Hub Transport organization configuration properties in the Exchange Management Console. When you modify an organizational limit in Exchange 2007 SP1, the new value is automatically copied to the corresponding global limit.

The following table shows the connector limits.

Connector limits

Source Parameter Version Default value

Set-ForeignConnector

MaxMessageSize

Exchange 2007 RTM and Exchange 2007 SP1

Unlimited

Set-ReceiveConnector

MaxHeaderSize

Exchange 2007 RTM and Exchange 2007 SP1

64 KB

Set-ReceiveConnector

MaxMessageSize

Exchange 2007 RTM and Exchange 2007 SP1

10 MB

Set-ReceiveConnector

MaxRecipientsPerMessage

Exchange 2007 RTM and Exchange 2007 SP1

200

Set-SendConnector

MaxMessageSize

Exchange 2007 RTM and Exchange 2007 SP1

10 MB

Set-AdSiteLink

MaxMessageSize

Exchange 2007 SP1

Unlimited

Set-RoutingGroupConnector

MaxMessageSize

Exchange 2007 SP1

Unlimited

The following table shows the server limits.

Server limits

Source Parameter Default value

Transport rule on an Edge Transport server that only applies to the specific server

AttachmentSizeOver

Not configured

Set-TransportServer on a Hub Transport server or Edge Transport server

PickupDirectoryMaxHeaderSize

64 KB

Set-TransportServer on a Hub Transport server or Edge Transport server

PickupDirectoryMaxRecipientsPerMessage

100

Outlook Web Access Web.config file on a Client Access server

maxRequestLength

30000 KB

The following table shows the user limits.

User limits

Source Parameter Default value

Set-DistributionGroup

MaxReceiveSize

MaxSendSize

Unlimited

Set-DynamicDistribution Group

MaxReceiveSize

MaxSendSize

Unlimited

Set-Mailbox

MaxReceiveSize

MaxSendSize

RecipientLimits

Unlimited

Set-MailContact

MaxReceiveSize

MaxSendSize

MaxRecipientPerMessage

Unlimited

Set-MailPublicFolder

MaxReceiveSize

MaxSendSize

Unlimited

Set-MailUser

MaxReceiveSize

MaxSendSize

RecipientLimits

Unlimited

You can set different message size limits for the same message component, such as the maximum message size, at different levels in the Exchange organization. When different message size limits are applied to the same message component, Exchange 2007 uses an order of precedence to enforce the message size limit that is imposed on the same message component.

For example, the recipient will receive a message that was sent by a particular sender if the following conditions are true:

  • An organization-wide send and receive message size limit of 10 MB is imposed on the Exchange 2007 organization.
  • A particular sender's mailbox has a send message size limit of 20 MB.
  • The recipient's mailbox has a receive message size limit of 20 MB.

Generally, it is better to maximize the restrictiveness of your message size limits. You should base any exceptions on a proven need to exceed the established size limits, and you should put those limits as close as possible to the objects that must exceed the established size limits. This strategy helps make sure that messages in the transport pipeline are rejected as early as possible if they violate message size limits. It is a waste of system resources to set a high message size limit at the Exchange organization level, allow a message to enter the Exchange organization, and then reject the message at the last stage of delivery because of a violation of a message size limit.

The tables in the following sections present scenarios that demonstrate how you can apply various message size limits in Exchange 2007 RTM and in Exchange 2007 SP1.

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Edge Transport server Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

noteNote:
The MaxReceiveSize and MaxEnvelopeReceiveLimit parameters are not used on an Edge Transport server. Use the message size limits on the Send and Receive connectors that are configured on an Edge Transport server to control the size of messages processed by the server.

Anonymous senders are always subject to the message size limits on the Receive connector that accepts messages from the Internet.

The default value of the MaxRecipientsPerMessage setting on the Receive connector is 200 recipients. If the number of recipients is exceeded for an anonymous sender, the message is accepted for the first 200 recipients. Most SMTP messaging servers will detect that a recipient limit is in effect. The SMTP messaging server will continue to resend the message in groups of 200 recipients until the message is delivered to all recipients.

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Connector on Edge Transport server

Send connector

MaxMessageSize

10 MB

10 MB

Connector on Hub Transport server

Receive connector

MaxRecipientsPerMessage

200

200

Connector on Hub Transport server

Receive connector

MaxMessageSize

10 MB

10 MB

Connector on Hub Transport server

Receive connector

MaxHeaderSize

64 KB

64 KB

Recipient

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxReceiveSize

Unlimited

Unlimited

All Hub Transport servers in the organization

Transport rule

AttachmentSizeOver

Not configured

Not configured

Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

An X-header that is named X-MS-Exchange-Organization-OriginalSize: is inserted into the message header. Any Hub Transport servers that are involved in the future delivery of the message will use this value for the message size. Conversion encoding and agent processing can increase the size of the message as it flows through the Exchange organization.

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Sender

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxSendSize

Unlimited

Unlimited

Recipient

Mail contact

MaxRecipientPerMessage

Unlimited

Unlimited

Recipient

Mailbox

Mail user

RecipientLimits

Unlimited

Unlimited

Recipient

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxReceiveSize

Unlimited

Unlimited

All Hub Transport servers in the organization

Transport rule

AttachmentSizeOver

Not configured

Not configured

Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

In Exchange 2007 SP1, you can set a maximum message size limit on an Active Directory site link or a routing group connector. For more information, see How to Configure Message Size Limits for Internal Routing.

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Sender

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxSendSize

Unlimited

Unlimited

Connector

Send connector

MaxMessageSize

10 MB

10 MB

Connector

Receive connector

MaxRecipientsPerMessage

200

200

Connector

Receive connector

MaxMessageSize

10 MB

10 MB

Connector

Receive connector

MaxHeaderSize

64 KB

64 KB

Recipient

Mail contact

MaxRecipientPerMessage

Unlimited

Unlimited

Recipient

Mailbox

Mail user

RecipientLimits

Unlimited

Unlimited

Recipient

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxReceiveSize

Unlimited

Unlimited

All Hub Transport servers in the destination organization

Transport rule

AttachmentSizeOver

Not configured

Not configured

Destination Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Destination Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Destination Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

If a specific Receive connector is configured in the destination Active Directory forest to accept messages from the source Active Directory forest, that specific Receive connector should have the ExchangeServers permission group and the ExernalAuthoratative authentication method assigned. This permission group contains the Ms-Exch-Bypass-Message-Size-Limit permission that allows messages to flow through the Receive connector without checking the message size. The message is still be subject to organization, transport server, sender, and recipient limits that are defined in the destination Active Directory forest.

For more information, see Configuring Cross-Forest Connectors.

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Sender

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxSendSize

Unlimited

Unlimited

Recipient

Mail contact

MaxRecipientPerMessage

Unlimited

Unlimited

Recipient

Mailbox

Mail user

RecipientLimits

Unlimited

Unlimited

Recipient

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxReceiveSize

Unlimited

Unlimited

All Hub Transport servers in the organization

Transport rule

AttachmentSizeOver

Not configured

Not configured

Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Sender

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxSendSize

Unlimited

Unlimited

All Hub Transport servers in the organization

Transport rule

AttachmentSizeOver

Not configured

Not configured

Connector

Foreign connector

MaxMessageSize

10 MB

10 MB

Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Server

Transport server

PickupDirectoryMaxHeaderSize

64 KB

64 KB

Server

Transport server

PickupDirectoryMaxRecipientsPerMessage

100

100

Server

Transport rule

AttachmentSizeOver

Not configured

Not configured

Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Server

Transport Rule

AttachmentSizeOver

Not configured

Not configured

Organization

Transport configuration

MaxReceiveSize

Unlimited

10 MB

Organization

Transport configuration

MaxRecipientEnvelopeLimit

Unlimited

5000

Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

 

Scope Source Parameter Default value in Exchange 2007 RTM and Exchange 2007 SP1

Sender

Distribution group

Dynamic distribution group

Mailbox

Mail contact

Mail-enabled public folder

Mail user

MaxSendSize

Unlimited

Connector on Hub Transport server

Send connector

MaxMessageSize

10 MB

Connector on Edge Transport server

Receive connector

MaxRecipientsPerMessage

200

Connector on Edge Transport server

Receive connector

MaxMessageSize

10 MB

Connector on Edge Transport server

Receive connector

MaxHeaderSize

64 KB

 

Scope Source Parameter Default value in Exchange 2007 RTM Default value in Exchange 2007 SP1

Edge Transport server Organization

Transport configuration

MaxSendSize

Unlimited

10 MB

noteNote:
: The following parameters are not used on an Edge Transport server. Use the message size limits on the Send and Receive connectors that are configured on an Edge Transport server to control the size of messages processed by the server.
•MaxReceiveSize
•MaxEnvelopeReceiveLimit

The following list shows the types of messages that are generated by a Hub Transport server or an Edge Transport server and exempted from all message size limits:

  • System messages
  • Agent-generated message
  • Delivery status notification (DSN) messages
  • Journal report messages
  • Quarantined messages

However, these messages are still subject to the organizational MaxRecipientEnvelopeLimit that is configured by using the Set-TransportConfig cmdlet in the Exchange Management Shell.

The primary difference in message size limits between Microsoft Exchange Server 2003 and Exchange Server 2007 is in the handling of recipient limits. Exchange 2007 treats a distribution group as one recipient. Exchange 2003 treats each member of the expanded distribution list as one recipient. This change was implemented to avoid the partial message delivery scenarios that may occur in Exchange 2003.

Partial message delivery occurs in Exchange 2003 if the number of individual recipients and the recipients that are contained within the distribution list exceeds the specified recipient limit. The total number of message recipients isn't known until after distribution list expansion. Message delivery occurs as the distribution list is expanded until the number of recipients reaches the specified limit. The remaining recipients don't receive the message, but at least the sender receives a non-delivery report (NDR) for each unsuccessful delivery. However, if delivery failure reporting is disabled for the distribution list, the remaining recipients wouldn't receive the message, and the sender would not know who didn't receive the message.

To ensure that you are reading the most up-to-date information and to find additional Exchange Server 2007 documentation, visit the Exchange Server TechCenter.
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