Alert notifications from Mackerel can be sent via email.
The notification will include a link to the alert, the service or role to which the offending host belongs, and any associated graphs.
Adding email alert notifications
To add a new Email notification channel, click on “Monitors,” then “Channel Settings,” then “New Channel”. Choose Email notification from the list of integrations and give the new notification channel a name. (e.g. "email to team")

You can select individual email addresses or users belonging to an organization as recipients of emails.