When Premium Antispam is enabled, connection timeout may occur and emails are queued on the sending server.
Connection timeout errors occur due to delay introduced into SMTP session for Premium Antispam scanning.
Possible solution is to adjust the Maximum Transmission Unit (MTU) of sending SMTP server.
Lower the MTU value makes smaller packets. This helps improve the performance and avoid the timeout to occur. For details on how to configure it on Windows environment, contact Microsoft support for assistance.
Another workaround solution is to disable Premium Antispam scanning between authenticated SMTP servers.
In SMSMSE 6.5.1 and earlier, Antispam scanning on authenticated SMTP sessions is disabled by default, these steps do not need to be taken if you are running 6.5.1 or earlier.
To edit the registry:
1. Exit all open programs
2. On the Windows taskbar, click Start > Run
3. In the Open box, type the following text: regedit and click OK
4. In the Registry Editor, create the following key:
For 32 bit systems:
For 64 bit systems:
(Where <version number> indicates either 6.0 or 6.5 the first two digits in your installed program version.)
5. In the right pane, right-click the blank area, and then click New > DWORD Value.
6. Give the value the following name:
7. In right pane, right-click DoAntiSpamOnAuthSessionsBool, and then click Modify.
8. In Value Data, type 0
9. Exit the Registry Editor.
10. Restart the Symantec Mail Security Exchange service.
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