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The SMTP Service, Abuse tab:

Large Message Safety

Sometimes a denial of service attack may be made against the Mailtraq server by sending a very large message - which may be Gigabytes in size - hoping to fill up the hard disk or some other resource. Mailtraq can be configured to place a limit on the size of inbound mail. This is different from other size limits within the system, as when this limit is reached, the connection to the sending mailserver is immediately broken, preventing the system from being overwhelmed by the attack. The nature of the message is remembered, so if it is presented again (as would be expected when the connection is broken in this way), Mailtraq can then issue a permanent rejection message. 


If Mailtraq determines that a message in the process of being delivered has exceeded the specified size limit, it generates a key which identifies that message, then immediately rejects the message by disconnecting its socket. If Mailtraq detects that a recently rejected message is being re-offered for delivery by the same sending client, the message is summarily rejected.

Mailtraq does not apply the Large Message Safety restrictions to messages being received from addresses or address specifications which appear in the whitelist on this tab (which can be edited by clicking on Exceptions).


Enable Large Message Safety
If this check box is enabled, Mailtraq monitors the size of all messages handled by this service instance.

Abort messages over
Enter the maximum size of message which Mailtraq should accept before activating Large Message Safety into the edit box provided.

Enter the addresses from which Mailtraq should accept messages of any size. Wildcards can be used to include complete domains, * for example, will allow messages of any size to be received from any user at

The key generated consists of the arguments given by the connecting SMTP system to the HELO, MAIL and RCPT verbs. The key cannot, therefore, identify an individual message uniquely and another message with exactly the same key may be rejected if offered to Mailtraq before the problem message is resent. This can result in the offending message being partially downloaded more than once, each time triggering Large Message Safety and generating a new key each time. Unless a significant denial of service (dos) attack is taking place, in which case Access Control can be employed to block the system(s) responsible, the problem message is eventually rejected.

Maximum Header Lines

Too many headers. The recommended number of header lines should not be more than 150, and current builds enforce that recommendation. Excessive headers can cause all sorts of transport problems to other mail services, and are a common indicator of spam - resulting in rejected messages.

This setting can be adjusted to suit your environment.

Large message header sizes are sometimes created by poorly formed mailing lists. Open mailing lists which expose the recipients email addresses to all are a great benefit to spammers who can easily 'harvest' the addresses.
Wherever possible mailing lists should be handled using the mailing list system - one is included with your Mailtraq. There is a special feature to facilitate mailing from a Personal Address Book...

Webmail HTTP Service Abuse control

See Webmail Setup - Limiting File Attachments




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