This solution applies to the Barracuda Spam Firewall when in use with Microsoft Exchange 2007/2010.
Your Outbound queue is building up due to high amount of deferred emails from recipient exchange server.
The outbound queue on the Barracuda is building up because mail is being deferred by the internal Exchange server. The error log of the Exchange server may give a an "insufficient system resources" error. Attempting to send a test email from the Barracuda will look like the example below, returning a 452 error 'Insufficient system resources'.
This is caused by what is called 'backpressure' on the exchange server. There are several reasons this occurs ultimately it is caused by a lack of disk space where the JET partition (the partition that handles the exchange queue) is located.
Note: 126.96.36.199 should be replaced with the IP Address of the Exchange server in question:
# telnet 188.8.131.52 25
Connected to valid.domain.com (184.108.40.206).
Escape character is '^]'.
220 valid.domain.com Microsoft ESMTP MAIL Service ready at Fri, 23 Dec 2011 13:59:31 -0800
250 valid.domain.com Hello [220.127.116.11]
452 4.3.1 Insufficient system resources
221 2.0.0 Service closing transmission channel
Connection closed by foreign host.
- Ensure that the requisite amount of disk space on the drive is above 4GB.
- Also, ensure that this is the partition that is the location of the JET queue.
- Exchange also gives the option to disable backpressure completely.
- Once the requisite amount of disk space is cleared up, restart the Microsoft Exchange Transport service from the Services console, or by using the Restart-Service cmdlet
- (Restart-Service MSExchangeTransport).
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