A new study in Israel found that using emojis in your work emails makes you seem incompetent.  Using them at work won't affect whether a person thinks you are friendly or not.

Researchers in Israel surveyed 550 people in 29 different countries.  They had these people read work related emails, without know what person sent them, that had the exact same words but some of them included emojis.  The emails that had the emojis in them, the people rated them less competent than the emails without.

Moreover, the existence of the smiley face emoji on the email didn't translate into warmth or friendliness for the study participants.  Also, the researchers found that the emails without emojis got more in depth and descriptive return emails than the ones that included emojis.

The researchers think it's probably okay to use emojis with a co-worker you're good friends with, because they probably won't judge you for it. Or just play it safe and don't use them at work.