Reverse DNS does not match SMTP Banner

cPanel based server using Exim.

Issue: When using the “Test Email Server” tool at: https://mxtoolbox.com/SuperTool.aspx?action=smtp, the following issues are displayed:

Reverse DNS does not match SMTP Banner
Warning – Does not support TLS
15.465 seconds – Not good! on Transaction Time

This is commonly caused because Exim has been configured to introduce a delay in the SMTP transaction. The delay is to ensure the SMTP receiver will wait a few additional seconds for a connection when it detects spam messages in order to reduce inbound spam.

Solution: To test and ensure the reverse DNS matches the SMTP banner, etc. temporarily turn off the SMTP transaction delay. To do so, complete the following…

Navigate to:

Home >> Service Configuration >> Exim Configuration Manager >> Basic Editor >> ACL Options

Find:

Introduce a delay into the SMTP transaction for unknown hosts and messages detected as spam” and change the setting to “Off“.

Click “Save”, this will save the setting and restart Exim.

Return to MXtoolbox (or any other similar tool) and test again. After completing tests, restore the delay.

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