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Understanding message size limits

[Cette rubrique est une documentation préliminaire et peut être modifiée dans les versions ultérieures. Des rubriques vides sont incluses comme espaces réservés. N’hésitez pas à nous transmettre vos commentaires. Envoyez-nous un e-mail à l’adresse ExchangeHelpFeedback@microsoft.com.]  

S’applique à :Exchange Server 2016

Learn how administrators can apply limits to messages in an Exchange 2016 organization.

You can apply limits to messages that move through your organization. You can set the maximum size of an entire message as a whole, or the size of individual parts of a message, or both. For example, you could restrict the maximum size of the message header or attachments, or set a maximum number of recipients that can be added to the message. You can apply these limits to your entire Exchange organization, to specific mail transport connectors, specific servers, and to individual mailboxes.

This topic only talks about message and recipient size limits. If you want to know more about how to control how many messages are sent over time, how many connections are allowed over time, and how long Exchange will wait before closing a connection, see Understanding message rate limits and throttling.

As you plan the message size limits for your Exchange 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?

  • What is the mailbox quota for my organization, and how do the message size limits that I have chosen relate to the mailbox quota size?

  • Are there users in my organization who need to send or receive messages that are larger than the maximum allowed size?

  • Does my organization include other messaging systems or separate business units that require different message size limits?

This topic provides guidance to help you answer these questions and to apply the appropriate message size limits in the appropriate locations.

Contents

Types of message size limits

Scope of limits

Organizational limits

Connector limits

Server limits

Recipient limits

Order of precedence and placement of message size limits

Messages exempt from size limits

The following list describes the basic types of message size limits, and the message components that they apply to.

  • Whole message size limits   Specifies the maximum size of a message, which includes the message header, the message body, and any attachments. Exchange uses the custom X-MS-Exchange-Organization-OriginalSize: message header to record the original size of the message as it enters the Exchange organization. Whenever the message size is checked, 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 transport agent processing.

    Quelle que soit la limite de taille du message, vous devez définir une valeur supérieure à la taille réelle que vous souhaitez appliquer. Cela explique le codage Base64 des pièces jointes et autres données binaires. Comme le codage Base64 augmente la taille des messages d’environ 33 %, la valeur que vous spécifiez doit être d’environ 33 % supérieure à la taille réelle de message que vous voulez appliquer. Par exemple, si vous spécifiez une valeur maximale de taille de message de 64 Mo, vous pouvez vous attendre à une taille maximale réelle de message d’environ 48 Mo.

  • Attachment size limits   Specifies the maximum size of a single attachment in a message. The message might contain many smaller attachments that greatly increase its overall size. However, the attachment size limit applies only to the size of an individual attachment. While you can't limit the number of attachments on a message, you can use the maximum message size limit to control the maximum total of attachments on the message.

  • Recipient limits   Specifies the total number of recipients that are allowed in a message. This includes the total number of recipients in the To:, Cc:, and Bcc: fields. A distribution group counts as a single recipient.

  • Message header size limits   Specifies the maximum size of all message header fields in a message. The size of the message body or attachments isn’t 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 text character consumes 1 byte.

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The following tables show the message limits at the Organization, Connector, Server, and Mailbox levels, including information about how to configure the limits in the Centre d’administration Exchange (EAC) or the Environnement de ligne de commande Exchange Management Shell. Pour en savoir plus sur l’ouverture de l’environnement de ligne de commande Exchange Management Shell dans votre organisation Exchange locale, consultez la rubrique Ouverture de l’environnement de ligne de commande Exchange Management Shell.

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Organizational limits apply to all Exchange 2016 servers, Exchange 2013 Mailbox servers, and Exchange 2010 Hub Transport servers that exist in your organization. On Edge Transport servers, any organizational limits that you configure are applied to the local server.

 

Size limitDefault valueEAC configurationEnvironnement de ligne de commande Exchange Management Shell configuration

Maximum size of a message received

10 MB

Mail flow > Receive connectors > More options Icône Options supplémentaires > Organization transport settings > Limits tab > Maximum receive message size (MB)

Cmdlet: Set-TransportConfig

Parameter: MaxReceiveSize

Maximum size of a message sent

10 MB

Mail flow > Receive connectors > More options Icône Options supplémentaires > Organization transport settings > Limits > Maximum send message size (MB)

Cmdlet: Set-TransportConfig

Parameter: MaxSendSize

Maximum number of recipients in a message

500

Mail flow > Receive connectors > More options Icône Options supplémentaires > Organization transport settings > Limits Maximum number of recipients

Cmdlet: Set-TransportConfig

Parameter: MaxRecipientEnvelopeLimit

Maximum attachment size for a message that matches the conditions of the Transport rule

Not configured

Mail flow > Rules > Add Icône Ajouter > Create a new rule, or select an existing rule, and then click Edit Icône Modifier.

Click More options.

Use the condition Apply this rule if > The message > size is greater than or equal to, and enter a value in kilobytes (KB).

Cmdlets: New-TransportRule, Set-TransportRule

Parameter: AttachmentSizeOver

Maximum message size for a message that matches the conditions of the Transport rule

Not configured

Mail flow > Rules > Add Icône Ajouter > Create a new rule, or select an existing rule, and then click Edit Icône Modifier.

Click More options.

Use the condition Apply this rule if > The message > size is greater than or equal to, and enter a value in kilobytes (KB).

Cmdlets: New-TransportRule, Set-TransportRule

Parameter: MessageSizeOver

To see the values of these organizational limits, run the following commands in the Environnement de ligne de commande Exchange Management Shell:

Get-TransportConfig | Format-List MaxReceiveSize,MaxSendSize,MaxRecipientEnvelopeLimit
Get-TransportRule | where {($_.MessageSizeOver -ne $null) -or ($_.AttachmentSizeOver -ne $null)} | Format-Table Name,MessageSizeOver,AttachmentSizeOver

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Connector limits apply to any messages that use the specified Send connector, Receive connector, Delivery Agent connector, or Foreign connector for message delivery.

You can assign specific message size limits to the Active Directory site links in your organization. The Transport service on Mailbox servers uses Active Directory sites, and the costs that are assigned to the Active Directory IP site links as one of the factors to determine the least-cost routing path between Exchange servers in the organization.

You can assign specific message size limits to the Delivery Agent connectors and Foreign connectors that are used to send non-SMTP messages in your organization.

 

Size limitDefault valueEAC configurationEnvironnement de ligne de commande Exchange Management Shell configuration

Maximum size of a message sent through the Receive connector

36 MB

Mail flow > Receive connectors > EditIcône Modifier > General > Maximum receive message size (MB)

Cmdlets: New-ReceiveConnector, Set-ReceiveConnector

Parameter: MaxMessageSize

Maximum size of all header fields in a message sent through the Receive connector

256 KB

Not available

Cmdlets: New-ReceiveConnector, Set-ReceiveConnector

Parameter: MaxHeaderSize

Maximum number of recipients in a message sent through the Receive connector

Transport service on Mailbox servers

Default <ServerName>   5000

Client Proxy <ServerName>   200

Front End Transport service on Mailbox servers

Default Frontend <ServerName>   200

Outbound Proxy Frontend <ServerName>  200

Client Frontend <ServerName>  200

If the number of recipients is exceeded in a message from an anonymous sender (for example, an Internet sender), the message is accepted for the first 200 recipients. Most messaging servers will continue to resend the message in groups of 200 recipients until the message is delivered to all recipients.

Not available

Cmdlets: New-ReceiveConnector, Set-ReceiveConnector

Parameter: MaxRecipientsPerMessage

Maximum size of a message sent through the Send connector

10 MB

Mail flow > Send connectors > EditIcône Modifier > General tab > Maximum send message size (MB)

Cmdlets: New-SendConnector, Set-SendConnector

Parameter: MaxMessageSize

Maximum size of a message sent through the Active Directory site link

Unlimited

Not available

Cmdlet: Set-AdSiteLink

Parameter: MaxMessageSize

Maximum size of a message sent through the Delivery Agent connector

Unlimited

Not available

Cmdlets: New-DeliveryAgentConnector, Set-DeliveryAgentConnector

Parameter: MaxMessageSize

Maximum size of a message sent through the Foreign connector

Unlimited

Not available

Cmdlet: Set-ForeignConnector

Parameter: MaxMessageSize

To see the values of these connector limits, run the following command in the Environnement de ligne de commande Exchange Management Shell:

Get-ReceiveConnector | Format-Table Name,Max*Size,MaxRecipientsPerMessage; Get-SendConnector | Format-Table Name,MaxMessageSize; Get-AdSiteLink | Format-Table Name,MaxMessageSize; Get-DeliveryAgentConnector | Format-Table Name,MaxMessageSize; Get-ForeignConnector | Format-Table Name,MaxMessageSize

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Server limits apply to specific Mailbox servers or Edge Transport servers. You can set these message size limits independently on each Mailbox server or Edge Transport server.

 

Size limitDefault valueEAC configurationEnvironnement de ligne de commande Exchange Management Shell configuration

Maximum size for a message sent by Outlook sur le web clients

35 MB

Not available

You configure this value in web.config XML application configuration files on the Mailbox server. For more information, see Configuration des limites de taille de message propres au client.

Maximum size for a message sent by Exchange ActiveSync clients

10 MB

Not available

You configure this value in web.config XML application configuration files on the Mailbox server. For more information, see Configuration des limites de taille de message propres au client.

Maximum size for a message sent by Services Web Exchange clients

64 MB

Not available

You configure this value in web.config XML application configuration files on the Mailbox server. For more information, see Configuration des limites de taille de message propres au client.

The pickup directory that's available on Edge Transport servers and Mailbox servers also has messages size limits that you can configure. Typically, the pickup directory isn't used in everyday mail flow. It's is used by administrators for mail flow testing, or by applications that need to create and submit their own messages files. For more information, see Configurer le répertoire de collecte et le répertoire de relecture.

  • Maximum size of all header fields in a message file placed in the pickup directory: 64 KB.

  • Maximum number of recipients in a message file placed in the pickup directory: 100.

Recipient limits apply to a specific user object, such as a mailbox, mail contact, mail user, distribution group, or a mail-enabled public folder.

 

Size LimitDefault valueEAC configurationEnvironnement de ligne de commande Exchange Management Shell configuration

Maximum size of a message that can be sent to the specific recipient

Site mailbox provisioning policies: 36 MB

All other recipient types: unlimited

For mailboxes:

Recipients > Mailboxes > EditIcône Modifier > Mailbox features > Mail flow section > Message size restrictions section > View details > Received messages section > Maximum message size (KB)

For mail users:

Recipients > Contacts > EditIcône Modifier > Mail flow settings > Message size restrictions > View details > Received messages section > Maximum message size (KB)

This setting available in the EAC for other types of recipients.

Cmdlets:

Set-DistributionGroup

Set-DynamicDistributionGroup

Set-Mailbox

Set-MailContact

Set-MailUser

Set-MailPublicFolder

New-SiteMailboxProvisioningPolicy

Set-SiteMailboxProvisioningPolicy

Parameter: MaxReceiveSize

Maximum size of a message that can be sent by the specific sender

Unlimited

For mailboxes:

Recipients > Mailboxes > EditIcône Modifier > Mailbox features > Mail flow section > Message size restrictions section > View details > Sent messages section > Maximum message size (KB)

For mail users:

Recipients > Contacts > EditIcône Modifier > Mail flow settings > Message size restrictions section > View details > Sent messages section > Maximum message size (KB)

This setting available in the EAC for other types of senders.

Cmdlets:

Set-DistributionGroup

Set-DynamicDistributionGroup

Set-Mailbox

Set-MailContact

Set-MailUser

Set-MailPublicFolder

Parameter: MaxSendSize

Maximum number of recipients in a message that's sent by the specific sender

Unlimited

For mailboxes:

Recipients > Mailboxes > EditIcône Modifier > Mailbox features > Mail flow section > View details > Recipient limit section > Maximum recipients

This setting isn't available in the EAC for mail users.

Cmdlets:

Set-Mailbox, Set-MailUser

Parameter: RecipientLimits

To see the values of these limits, run the corresponding Get- cmdlet for the recipient type in the Environnement de ligne de commande Exchange Management Shell.

For example, to see the limits that are configured on a specific mailbox, run the following command:

Get-Mailbox <MailboxIdentity> | Format-List MaxReceiveSize,MaxSendSize,RecipientLimits

To see the limits that are configured on all user mailboxes, run the following command:

$mb= Get-Mailbox -ResultSize unlimited; $mb | where {$_.RecipientTypeDetails -eq 'UserMailbox'} | Format-Table Name,MaxReceiveSize,MaxSendSize,RecipientLimits

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The order of precedence for message size limits is the most restrictive limit is enforced. The only question is where that limit is enforced. The goal is to reject messages that are too large as early in the transport pipeline as possible. For example, it's a waste of system resources for the Internet Receive connector to accept large messages that are eventually rejected because of a lower organizational limit. Make sure that your organization, server, and connector limits are configured in a way that minimizes any unnecessary processing of messages. You do this by keeping the limits the same in all locations, or by configuring more restrictive limits where messages enter your Exchange organization.

Recipient limits between authenticated senders and recipients (typically, internal message senders and recipients) are exempt from the organizational message size restrictions. Therefore, you can configure specific senders and recipients to exceed the default message size limits for your organization. For example, you can allow specific mailboxes to send and receive larger messages than the rest of the organization by configuring custom send and receive limits for those mailboxes.

However, this exemption applies only to messages sent between authenticated senders and recipients (typically, internal senders and recipients). For messages sent between anonymous senders and recipients (typically, Internet senders or Internet recipients), the organizational limits apply. For example, suppose your organizational message size limit is 10 MB, but you configured the users in your marketing department to send and receive messages up to 50 MB. These users will be able to exchange large messages with each other, but not with Internet senders and recipients (unauthenticated senders and recipients).

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The following list shows the types of messages that are generated by Mailbox servers or Edge Transport servers that are exempted from all message size limits except the organizational limit for the maximum number of recipients that are allowed in a message:

  • System messages

  • Agent-generated message

  • Delivery status notification (DSN) messages (also known as non-delivery reports, NDRs, or bounce messages). However, you can use the ExternalDsnMaxMessageAttachSize and InternalDsnMaxMessageAttachSize parameters on the Set-TransportConfig cmdlet to limit the size of original messages that are included in DSN messages (hence, the effective size of the DSN message itself).

  • Journal report messages

  • Quarantined messages

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