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ListMessenger exceeds expectations as a well designed, easy to use, lightweight mailing list management solution for your website. ListMessenger is feature packed but because of its intuitive design remains simple to use and easy to maintain.
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What is the MX Lookup in the end-user tools for?

An MX Lookup (not available for Windows servers) is used to evaluate the e-mail address that the end-user provides. For example, if they enter, ListMessenger will check to ensure that has a valid mail exchanger record in their DNS. This is to ensure that the domain that the end-user entered is a) valid b) is able to accept e-mail. This function can possibly slow down the script by a split second or so, but also helps to prevent false e-mail addresses in your list.