Each event on a Teamup calendar can be shared via the Share menu, on a browser and from the Teamup app.
One of the default sharing options is email. When you choose this sharing option, Teamup will open a draft email with pre-populated event details. You can then add recipients, make any additions or changes to the message, and send the email.
Teamup uses the email client that is set as your default email. The default email setting is controlled in your OS settings or your device settings. Teamup doesn't control and can't change your default email setting.
If you want a different email client to open when you share an event by email, change the default email setting in your operating system or device settings.