Unfortunately this has been the weak point with what is my all time favorite email client. Frequently the alert is broken with new released. All of these (I think) are due to it being a 3rd party contribution and they don't update to stay up to date with new requirements.
What is the biggest outpoint here is that the Moz team is not including it by default. After the last update I learned that hard way that no sounds were going to be played anymore. It appears to be the only GUI mail client without a new mail alert.
For me it can easily costs money each time I'm not alerted to new emails. But I'm done with using extensions/plugins as they are too frequently not maintained for very long.
😞 😞 😞 😞
