Odd issue with Nextcloud Sync - Emails read?


I have a client experiencing an odd issue with his emails showing “read” via Hubspot Tracking in San Jose, Portland and other cities when using Nextcloud Sync for Windows app.

Basically, whenever he sends emails he can view when the person reads it. Plus it shows the geographic region the email was read in (I’m guessing based off the IP address). Apparently it’s been working correctly but since he installed the Nextcloud app, from my suggestion, this has been happening.

Is there any way the two can be connected? I don’t have any plausible explanation.

More info if applicable:
Hosts email through BlueHost (IMAP)
Nextcloud is installed via Docker on Synology
Sends email from Outlook
We setup automated emails from Nextcloud but it’s from a different user/email account

Thank you,

So your client tracks his e-mails to get information when and where it was read. And he uses Nextcloud synchronisation on his Windows phone at the same time? Or is this an issue the the notification mails of Nextcloud and his mail tracking, and the Nextcloud mails show as read or other mails show as read?
Perhaps my difficulties come from that I don’t know the other services and it might be clear for someone using them.