You already did, by @name mentioning a person on a post, they get an email notification, just be aware of the @name mentioning policy to avoid a misuse of this feature.
What is @name mentioning?
@name mentioning is when you type someone's username with an @ preceding it. Doing this sends a notification to the user. Depending on their settings, it may also send them an email message.
For example, with @JacqueHousteauGram in my text, Jacque here will be dynamically notified in community (and via email if he's configured for it).
Please don't use this feature excessively
In general, it is considered bad form to @name mention someone not otherwise engaged in the conversation.
Why should I limit how much I @name mention others?
It can be annoying
Active people who were being frequently mentioned in topics were first to request that this practice be minimized…