Mail Tracking Issues Within Own MailSpring Mailboxes

This subject might sound a bit mysterious, I admit. After subscribing to MailSpring, I decided to test the link-tracking feature with my own set of mailboxes. I have about eleven mailboxes in MailSpring, a mix of private mailboxes and several for volunteer work I do for various organizations. So, I turned tracking on and sent some emails between those addresses. Surprisingly, nothing happened. I opened messages, but they remained marked as unopened in the sending mailbox. At this point, I was a bit disappointed. Had I bought a “kat in de zak” (a pig in a poke)?

It wasn’t until I sent emails to others and started to receive notifications that the messages were opened. Apparently, it only works when you send emails to mailboxes that you do not manage within your MailSpring environment.

Is this observation correct?