It used to be, on some mail readers, that "opening" an email message could unleash Pandora's Box, in terms of interpreting HTML, downloading images, attachments or whatever. I sincerely doubt that is even the case for the major providers such as Outlook or Gmail. And yeah, per comments downthread, my Android Messages app has "read/unread" and that's really the only thing that "opening a text" changes. There's no additional execution or activation like opening or executing a file.
> It used to be, on some mail readers, that "opening" an email message could unleash Pandora's Box, in terms of interpreting HTML, downloading images, attachments or whatever.
That's still true for both email and text messages.
Back in the day, some systems used to acknowledge the request for a read receipt by default giving them the ability to determine if a number was actively watched.
Hopefully everything has it disabled by default these days.
