It is important to keep in mind that:
• Emojis are not all supported; they are more and more supported, but not 100%.
• Not all symbols are supported, so you need to test thoroughtly.
• When the symbol cannot be displayed, a square will take its place (☐).
As for message reception, or spam, there is no way we can be certain that the message was received or not, and nothing garantees the delivery of messages. In addition, for delivery, each domain is configured differently, and so are inboxes and anti-spam filters. So each company and client is probably subject to different rules that either accept or decline special characters such as emojis.
So to reply to the question ... "Yes you can use them, BUT test!"
Other links of interest
- Divers symboles and Dingbats --> these symbols are accepted by Dialog Insight
- Popular Emojis for Your Newsletter Subject Lines
So our best piece of advice is "TEST, TEST, and TEST again!"