MTA Stress and Stress Mode event log

Why You Should Care and What You Should Know

Q: What does MTA stand for?

MTA refers to the Mail Transport Agent. This is the process/program in your SpammerTrap that is responsible for accepting and delivering email.

Q: What is MTA Stress?

Each SpammerTrap model has a different process limit to help maximize the efficiency of the device. An MTA stress alert is generated, in the form of an entry in the event log, when a SpammerTrap MTA reaches its process limit. Usually this is caused by spikes in email being processed by the SpammerTrap, such as email attacks, for example.The % (percentage) shows you what percentage of incomming email processes are under stress.  100% stress would mean that for a certain server, all available processes are in stress mode.

Q: Will email still be processed while in a stress state?

With SpammerTrap, yes. Even during MTA stress the SpammerTrap receives and processes emails. SpammerTrap's intelligent "stress-adaptive" behavior allows the appliance to continue to function even under unusually high loads, a unique feature that maximizes efficiency and significantly reduces the risk of system failure. when under stress mode certain DOS and rate limiting settings are automatically adjusted.  Incoming email from spammers or large email providers may be delayed. By contrast, MTA stress can cause other email security products to crash or become unresponsive.

Q: Will I be notified again when the system exits its stress configuration and returns to normal?

No, when the system detects the overall load on the MTA to be at normal limits again, normal mode will resume transparently.  You can check stress mode by looking at the 'Stress' status (Y/N) and percentage on the home status screen.

Q: What can I do to stop or fix MTA stress?

Infrequent MTA stress alerts don't indicate a problem. However, if you see Stress log entries in your event log, and experience reports of long delays in email delivery, it could point to a potential problem as described below:

Stand-Alone Appliance:  Generally, an increase in alerts indicates that your unit is reaching the upward limits of performance. At this point, it may be prudent to upgrade to a larger model, or to consider a load-balanced deployment.

Clusters and VPS: If you are receiving MTA stress alerts from only one SpammerTrap node, it could mean that your current clustering configuration is not properly load-balanced. Make sure that all of your domains MX records are set according to recommendations. Contact SpammerTrap Support for further assistance. If you are receiving these alerts from all of your clustered nodes, it may be prudent to upgrade to a larger model or to consider a rebalanced deployment.

All Servers: If you are under a DHA (Dictionary harvest) or BackScatter attack from multiple locations, Stress mode may be automatically invoked to allow legitimate email to pass through.

For any further assistance, please contact your SpammerTrap Support team at This e-mail address is being protected from spambots. You need JavaScript enabled to view it