Exchange Message Size Limits

While traveling trough your Exchange organization or beyond, e-mail messages may be imposed to all sorts of limitations. One of these limits is the message size limit, which can be set on the following levels:

  • Organizational Level
  • Send Connector
  • Receive Connector
  • AD Site Links
  • Routing Group Connectors
  • Individual

The path evaluated is as follows: User Send Limit > Receive Connector > Organization Checks > Send Connector > User Receive Limit

In general, the lowest size limit on an e-mail route determines if a message can be successfully transported from sender to the recipient. Exception is the individual setting which can override the other settings for internal messages. Strategy is to define limits where appropriate and as soon as possible. It’s a waste of resources to accept a message, send it throughout the organization via several hops, to finally reject the message because the recipient has a maximum receive size limit.

Organizational Level
The message size limits on the organization level can be set through the Exchange Management Console via Organization Configuration > Hub Transport > Global Settings by opening the Properties of Transport Settings:

TransportSettings

Of course, you can also view the settings using the Exchange Management Shell using Get-TransportConfig, e.g.

TransportSettings-EMS

As you can see, the default value in Exchange 2010 is 10240 (10 MB) for both receive as well as send message sizes. If you require a higher value, for example to enable people to send and receive larger attachments, you can use the EMC or Set-TransportConfig:

Set-TransportConfig –MaxReceiveSize 25MB –MaxSendSize 25MB

As you might expect, MaxReceiveSize applies to receive connectors, MaxSendSize applies to send connectors. Valid range for this setting is anywhere in the range between 64KB and 2GB or Unlimited. When set to Unlimited (which once was the default values in Exchange 2007 RTM), no limit will be imposed. I don’t recommend using Unlimited since it can lead to service disruption caused by processing large messages.

Send Connector
The message size limits on a send connector can be set through the Exchange Management Console via Organization Configuration > Hub Transport > Send Connectors by opening the Properties of the Send Connector:

SendConnector-EMC

You can also use Get-SendConnector to view the setting:

SendConnector

The default maximum sending message size for Exchange 2007/2010 send connectors is 10 MB. If you want to be able to send larger messages over this send connector, you can use the EMC or Set-SendConnector:

Set-SendConnector –Identity Internet –MaxMessageSize 25MB

Valid range for this setting is anywhere in the range between 64KB and 2GB or Unlimited.

Receive Connector
The message size limits on a send connector can be set through the Exchange Management Console via Server Configuration > Hub Transport by opening the Properties of the Receive Connector in the Receive Connectors pane:

ReceiveConnector-EMC

You can also use Get-ReceiveConnector:

ReceiveConnector

The default maximum receiving message size for receiving messages for Exchange 2007/2010 receive connectors is 10 MB. If you want to be able to receive larger messages over this receive connector, you can use the EMC or Set-ReceiveConnector:

Set-ReceiveConnector –Identity “MAIL1\Default MAIL1” –MaxMessageSize 25MB

Valid range for this setting is anywhere in the range between 64KB and 2GB or Unlimited.

AD Site Link
Messages travelling between Hub Transport servers are subject to AD site link limits. By default site links have no message size limit. You can view AD site link settings using Get-AdSiteLink or use Set-AdSiteLink to configure MaximumMessageSize when required.

ADSiteLink

Note that Hub Transport servers use least cost routing to route messages. When a message exceeds a site link limit, the message will not be delivered. Hub Transport servers will not try to deliver the message using a different route.

Routing Group Connectors
In a co-existence scenario you might have routing group connectors connecting Exchange 2007/2010 to an Exchange 2003 environment. Routing group connectors have no maximum message size limit by default.

To inspect a routing group connector maximum message size settings, use Get-RoutingGroupConnector:

Get-RoutingGroupConnector <ConnectorID> | FL Name, *Max*

To configure a maximum message size limit on a RGC use Set-RoutingGroupConnector:

Set-RoutingGroupConnector <ConnectorID> -MaxMessageSize 25Mb

Individual
You can create exceptions for the MaxReceiveSize and MaxSendSize values for mailbox users, mail-enabled contacts and distribution groups. By default no limits are imposed (i.e. Unlimited). To inspect the settings for a mailbox user, navigate to Recipient Configuration > Mailbox and open the Properties of the User. Activate tab Mail Flow Settings and open the Properties of the Message Size Restrictions settings:

UserMessageSizeSettings

or use the related cmdlet, e.g. Set-Mailbox UserID –MaxSendSize 1GB –MaxReceiveSize 1GB:

UserMessageSizeSettings-EMS

If you set an individual maximum send or receive size setting higher than the organization or connector limits, the individual setting will override those limits when the message is send internally, e.g the recipient resides in the same organization. This way you can create exceptions for certain individuals which require a higher message size limit.

17 thoughts on “Exchange Message Size Limits

  1. Pingback: Limites de anexo no Exchange 2010 « Rodrigo Rodrigues .:. www.andersonpatricio.org

  2. Quick question
    Do Organizational Level settings override settings on the server send or receive connectors
    e.g global max receive size is 20MB and receive connector is 10MB. But we can receive email over 10MB o.k

    • Hi Adrian,

      The lowest number dictates behavior. In your case, messages up to 20MB will be transported but on that specific receive connector a 10MB limit applies.

  3. Hi mate,

    We have two sets of users: Standard users and VIP users.
    We want standard users to be able to send mail externally with a limit of 10MB and for VIP users to be able to send mail externally with a limit of 15MB.

    We have only one Internet Send Connector. How do we configure Exchange to allow the two sets of users to send mail externally with their limits?

    I know we can edit the ‘Message Size Restrictions’ on the inividual mailbox properties, but that is only for internal messages as you stated above.
    How do we set this for external users?

    Thanks in Advance
    Ranz

    • Two options, both starting with setting all organizational settings e.g. transport config, connectors to the VIP limit and in addition restrict standard users by either:
      * imposing lower limit using MaxSendSize and MaxReceiveSize;
      * using transport rules to restrict non-VIP users from sending messages over the standard limit.

      I’d prefer the 2nd one.

  4. Hi Michel,

    Thanks for your response.

    How would I go about setting the transport rule? What Condition would I select?

    Also, as I have my VIP users in a specific VIP_MBDatabase (Mailbxox Database), In Transport rules, is there anywhere I can set per mailbox databases?

    Thanks

  5. I believe that it is very important to make the distinction between internal Exchange and Internet in/outbound mail limits. Your last paragraph should read more like this (of course feel free to verbally slap me around if I’m mistaken):

    “If you set an individual maximum send or receive size setting higher than the organization or connector limits, the individual setting will override those limits when the message is send internally, e.g the recipient resides in the same organization. This way you can create exceptions for internal mail for certain individuals which require a higher message size limit. This exception does not apply to mail entering or leaving the organization. You still have to change your Organizational limits accordingly.”

  6. Pingback: Meddelandestorlek i Exchange 2010 | JohanPersson.nu

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  8. If on is using the POP3 connector (that comes with SBS 2008 and 2011, for example) you must increase the Sharepoint Fax Receive connector (under the EMC Server, Hub, Receive Connectors) as well as all the other changes mentioned above. Some folks say they need to turn off the content filter too but I have not found that to be necessary.

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  10. Hi,

    How I can set personal default size settings to all users, because there are more than 1000users and many users have limits set personaly on mailbox, I don’t want to enter user by user and view if there is or no limits set.

    • PowerShell?

      First, get the mailboxes you want to process.
      All:
      $M= Get-Mailbox -Resultsize Unlimited
      or filtered:
      $M= Get-Mailbox -Resultsize Unlimited | Where { $_.MaxSendSize -ne $null}

      then apply limit
      $M | Set-Mailbox –MaxSendSize 100MB –MaxReceiveSize 100MB
      or unlimited:
      $M | Set-Mailbox –MaxSendSize Unlimited –MaxReceiveSize Unlimited

      Does that answer your question?

  11. Hi Michael,

    At the Org level, we have a transport limit of 10mb per message. We have a handful of users that we have increased that setting at the mailbox level. As I understand it, the mailbox setting overrides the Org transport setting. I also understand that this scenario is for internal emails only. We had a user that needed to send messages larger than 10mb outbound to the internet. I read up, and changed the Send Connector setting in Org – Hub Transport – Send Connectors to 20mb, the same as the setting on this individual’s mailbox. However, when she tries to send a message to an external recipient, she get’s an NDR saying the message cannot be sent because it is larger than the allowed limit, 10mb.

    Is there another setting that I need to change in order for this scenario to work? Thank you!

    • No. That 100% increase should suffice to compensate for the added MIME bloat (~37%).
      I assume you have checked the return message is from your Exchange environment and that there is no hygiene appliance sitting in between with enforced limits?

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