API to Trigger Email or Update Lead

Is it currently possible to use the API to be trigger an email be sent when an activity is triggered in another system.



For example:

A purchase is completed and you want to trigger a post sale sequence.



Alternatively there could be fields that get updated with product was purchased and that update could be a trigger.



Please advise.

Is it currently possible to use the API to be trigger an email be sent when an activity is triggered in another system.

For example:
A purchase is completed and you want to trigger a post sale sequence.

Alternatively there could be fields that get updated with product was purchased and that update could be a trigger.

Please advise.