To forward emails to tasks, you need to forward the email from the same email account associated with your 24me account. Forward emails to task@twentyfour.me and the task will appear on your calendar. Tasks may take up to one minute to be processed and listed in 24me. Even if the email is on another email account, you can still forward it using your email address which is associated with 24me by choosing which email account it comes from in your email settings.
https://24me.zendesk.com/hc/en-us/articles/360001136431-Email-to-Task-Premium-feature-