You can avoid your coworkers misinterpreting the tone of your emails by outright stating how you feel about their work. Don't be coy, but be respectful. After all, being direct is one of the key ways to better communicate at work.
Image from Startup Stock Photos
Andrew Brodsky gives a great example of how indicating your emotions upfront makes for a clearer — and ultimately more productive — email. The original example email is from a manager to their employee with feedback on a recent project:
The intro of the commercial needs to be redone. I'm sure that's the client's doing and you will handle it :). Warm Regards, [Manager's Name].
The manager's message tried to skirt around hurting the employee's feelings over the poor quality of a project by blaming the client. Despite the smiley face, the employee interpreted this message as condescending since the manager knew they had done the intro, not the client.
Instead, the manager should have lead with how they felt about the employee's work overall and then made the ask for reworking the intro, like this:
I am very happy with your work so far. I think the intro could be improved, though; would you mind giving it another shot?
With the rewritten message, the employee knows their work is appreciated and is ready to address their manager's concerns on the project. You can also use this method when giving collaborative feedback to colleagues, even if they're not someone you supervise. Keep this approach in mind to prevent your own messages from being misunderstood (and from causing tension).
The Dos and Don'ts of Work Email, from Emojis to Typos [Harvard Business Review]