Users sending messages with attachments to recipients hosted in Exchange servers can end up receiving bounce mails due these attachments.

Our Support Engineers support hundreds of Exchange servers for web hosts, web designers and other online businesses.

In these servers, we’ve seen huge attachments or unsupported attachments formats causing email error 552.

The error message seen by the senders in the bounce mail in cases of huge attachment size limit would be error 552 – ‘5.3.4 Message size exceeds fixed maximum message size’.

If the bounce happens due to the content of the attachment, the error message would be similar to error 552 – ‘5.7.0 Our system detected an illegal attachment on your message.’

What is email error 552 ‘5.3.4 Message size exceeds fixed maximum message size’

Every mail server has custom settings for the size of mails users can send and receive through it. These limits can either be global or individual-account specific or both.

To limit bandwidth usage, this email size limit is often restricted to a few MBs in most servers. If the email size exceeds that limit, it will be rejected by the mail server.

Error 552 ‘5.3.4 Message size exceeds fixed maximum message size’ is an email error commonly seen in bounce messages that generate from recipients using Exchange mail server.

In an Exchange server, there are mainly 4 settings for message size limitations:

a. Global value for the mail server
b. Receive and Send Connectors setting
c. SMTP Virtual Server setting
d. Individual user mailbox restriction

If the message size in the email exceeds any of these limits that are allowed for a particular email user account, it will be rejected with this error 552 message.

To resolve a valid email bouncing with error 552, these attachment limits have to be increased or adjusted appropriately.

But before we get into the detailed steps on how to increase these limits to accept valid user mails with attachments, we’ll see how these message size limits are to be calculated.

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How to determine the email message size limits?

In Exchange mail servers, content conversion happens for mails. Exchange server converts an internet/MIME message to MAPI/Exchange format, and vice versa for transmission.

After this content conversion process, the message size generally increases by about 30%. As a result, a message of 9 MB may fail to deliver to a server with size limit 10 MB.

Also, the precedence of the message size limits has to be noted before changing the settings. The maximum allowable message size for a server should be set as the organizational limit.

If the message is sent to or received to the server from a user on the Internet, this organizational limit will be applied to that mail.

But for internal users who send mail to each other after successful authentication, the user mailbox limit takes precedence over all other size restrictions.

So, for a server to accept messages from the internet with size around 15 MB, all the message limits should be set at 20 MB, considering the content conversion size.

How to fix error 552 ‘5.3.4 Message size exceeds fixed maximum message size’ in Exchange server

To accept mails of large sizes from valid senders, the message size settings have to be increased in the server. Here’s how to do it for each limit:

1. How to increase global message size settings

The global default message size limit for Exchange Servers 2007 to 2010 is 10 MB. To change this value, the steps are:

1. Open the Exchange Management Console.
2. Click on Organization Configuration -> Hub Transport.
3. Click on Global Settings -> Transport Settings.
4. On the Properties -> General tab, set the maximum send and receive size limits.

This is the organizational setting and would be applicable to all mails sent and received from that server over the internet.

Increase global message size limits in Exchange server

2. How to change message size limits for Receive connector

Receive connectors are the gateways through which all inbound messages are received to a mail server.

The maximum message size limit for a mail that can be received on a receive connector can be set by:

1. Open the Exchange Management Console
2. Click on Server Configuration -> Hub Transport
3. Select a Hub Transport server
4. Click on Receive Connectors
5. Choose the receive connector and Click on Properties
6. Click on the General tab and set the maximum message size

Setting a limit on receive connector can further limit the message size based on the sender’s IP address or type.

3. How to change message size limits for Send connector

Send connectors are configured to change the email sending behavior in server. To change the maximum message size limit on send connectors, do these steps:

1. Open the Exchange Management Console
2. Click on Organization Configuration -> Hub Transport
3. Click on Send Connectors
4. Choose a send connector and Click on Properties
5. Click on the General tab and set the maximum message size.

This limit is used to limit the size of outgoing mails from a server.

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4. How to increase message size settings for individual mail accounts

The individual mailbox settings can be changed from Exchange Administration Center (EAC). Here’s how to do it:

1. In the EAC, go to Recipients > Mailboxes.

2. Select the mailbox that you want to change the message size limits for, and then click Edit.

3. On the mailbox Properties page, click Mailbox Features.

4. Under Message Size Restrictions, change the following message size limits:

5. Sent messages - sets the maximum size of message that can be sent by the user. The value has to be set in KBs.

6. Received messages  - give the maximum size of messages that can be received by this user account in KBs.

7. Click OK and Save the changes.

User mailbox settings are usually set to limit or override the default global size of email messages sent between users within the same server.

All these email settings should be verified one by one to ensure that mails to the recipients are delivered successfully without bouncing with the error 552 ‘5.3.4 Message size exceeds fixed maximum message size’.