SMTPClient: ReceiveResponse: 452 4.3.1 Insufficient system resources

As the Event 15006 logged, please verify that the hard disk contains more free space than the threshold that has been configured for the Transport server. Please refer to: https://technet.microsoft.com/en-us/library/bb201658(v=exchg.160).aspx

If in the case, you cannot make the necessary disk space adjustments. Then we can choose to change the location of the queue database to a disk drive with sufficient free space. It can be done by following the following steps:

  • Begin by terminating the transport service
  • Go to the original queue folder (the one containing all the queue database and logs) and copy the files to the new desired directory.
  • Open notepad and open the file C:\Program Files\Microsoft\Exchange Server\V15\Bin—EdgeTransport.exe.config
  • Edit the following Keys:

<add key=”QueueDatabasePath” value=”C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue” />

<add key=”QueueDatabaseLoggingPath” value=”C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue” />

Note: The paths above need not be identical.

Hope it helps.