Only some emails logged

Hi,

I think this issue is more related to the other plugins than the actual mail logging as I have tried another logging plugin and that has similar results, but I was hoping someone here might be able to point me in the right direction.

I have a plugin installed called calendarista which takes online bookings and emails the admin and user.
We know that it is sending emails as the administrator is receiving the notifications, but we have had reports that some customers aren’t getting them.
So we installed this plugin to check on what was being sent.
It records all emails other than the ones from this plugin.

I looked through the plugin code and all emails are sent using the WordPress wp_mail() function.

If the plugin uses the native email sending methods, what could stop email logging plugins from being able to log the outgoing emails?

Thanks for any help!