The MailUp module for Drupal works with versions 6.x of Drupal. It has been successfully tested with Drupal 6.26 and MailUp versions from 7.4 to 8.0.
If you have a standard installation of Drupal please ensure that you have installed also the following:
Hence, Drupal status report (admin/report/status) should be similar to what you see below.
Modules to be installed on Drupal
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