Email reports are on Configuration->Email Alerts, on that page, after the SMTP config, there is a button there sends those email tests.
Do you get it every day, at the same time ? Is there a report attached, or just plain text ?
Maybe someone copied that email subject, made a report with that name, and configured as a scheduled email ? A bit far fetched, I know ... And in that case the Subject should be "[REP] Lansweeper Connection Test Email", not just "Lansweeper Connection Test Email"...
Besides that, maybe a LS bug ? I now that are issues with email reporting, when I upgraded from 5.x to 6 email reporting has not working, I had to convert all my configured reports "Alert Type" field to Directory and them back to E-mail so they would get get going...
Well, there is also the possibility that someone is going to that page and pressing the "Test" button...