Some message types in Mixpanel have limitations depending on your Mixpanel plan.
Push, Webhook and In-App messages
There is no limit on sending these types of messages per-se (i.e., there is no per message charge or extra fee) for sending push and email messages. However, a few things to keep in mind:
Messages can only be sent to users who have people profiles; under a free plan, you’re allotted 1,000 people profiles (see mixpanel.com/pricing for other people plan options).
Each message sent fires a "Notification Sent" event, which counts towards your monthly event quota. So, for example, if you were to send an email to 500 users, this would equate to 500 events (500 data points).
Additionally, if you’re planning to track open rate for email and push messages, this also fires a “Notification Open” event that also counts toward your monthly event quota.
At this time, Mixpanel users on a free account are limited to 150,000 email messages per month. Emails sent in excess of this limit will not be delivered.
Sending SMS messages via Mixpanel, you’re limited to 1,000 SMS/month (unless otherwise contractually agreed upon with Mixpanel). There is no extra charge for SMS messages sent to numbers outside the United States.