Exchange Size Limits: Understanding KB ID 0001368 and Resolving NDRs

If you’re experiencing issues with sending emails via Exchange, you may encounter an error message like the one below:

“The following files weren’t attached because adding them would cause the message to exceed the maximum size limit of {Size} MB: {File-Name}”

Or, when someone attempts to send a message to one of your mailbox users, they may receive an NDR with the following message:

“Remote Server returned ‘550 5.2.3 RESOLVER.RST.RecipSizeLimit; message too large for this recipient'”

These errors are usually caused by size limits set on the Exchange server, and they can be resolved by understanding the different size limits that apply to sending emails via Exchange.

TransportConfig Size Limits

One of the most common places where size limits are set is in the TransportConfig section of the Exchange server. To view these limits, use the following command:

Get-TransportConfig | format-list MaxSendSize, MaxReceiveSize

To change these limits, use the following command:

Set-TransportConfig -MaxSendSize 100MB -MaxReceiveSize 100MB

Send Connector Size Limits

Another place where size limits can be set is on the Send Connectors of the Exchange server. To view these limits, use the following command:

Get-SendConnector | format-list Name, name,maxmessagesize

To change these limits, use the following command:

Set-SendConnector “{connector-name}” -MaxMessageSize 100MB

Receive Connector Size Limits

The Receive Connectors of the Exchange server also have size limits that can be set. To view these limits, use the following command:

Get-ReceiveConnector | format-table Name, MaxMessageSize

To change these limits, use the following command:

Set-ReceiveConnector “{connector-name}” -MaxMessageSize 100MB

Mailbox Size Limits

Individual mailboxes can also have size limits set on them. To view these limits, use the following command:

Get-Mailbox -Identity “user-name” | format-table MaxSendSize,MaxReceiveSize

To set individual mailbox limits, use the following command:

Set-Mailbox -Identity “user-name” -MaxSendSize 100MB -MaxReceiveSize 100MB

Troubleshooting Tips

If the above steps do not resolve the issue, there are a few more troubleshooting tips you can try:

1. Check the OWA, EWS, and ActiveSync config files for maxRequestLength settings. These files are located in the ClientAccess folder of the Exchange installation.

2. Perform an IISRESET command to ensure that the new size limits take effect.

3. Check for any misconfigured AppPools in IIS on the CAS servers.

4. If the issue persists, check for any other size limits set on the Exchange server, such as the maximum message size limit set on the default frontend server.

Conclusion

In conclusion, understanding the different size limits set on an Exchange server is crucial in resolving issues with sending emails that exceed the maximum size limit. By using the commands and techniques outlined above, you can set individual mailbox limits, change send connector limits, and resolve NDRs caused by message size limits. Remember to always check for any misconfigured AppPools in IIS on the CAS servers, and perform an IISRESET command to ensure that the new size limits take effect.