When selecting the email shortcut (below your Name and Title) as an option to connect with a colleague, your phone/computer has a default email account to send that email through. However, this can be changed. The email option is visible through a colleague's Profile or through People Search.
From a Profile:
From People Search:
Tap the Ellipsis on the right side of the contact. Then you can choose email as an option.
To change the default email client follow the directions below.
Scroll down to select "Mail"
Scroll down to select "Default Account"
Choose your new default email client
On a Mac:
Choose Preferences from the Mail menu, then click General. Or, if you're prompted to set up an email account, add your account, then choose Preferences from the Mail menu.
Choose your email app from the ”Default email reader” pop-up menu.