In Crelate, you may have multiple email connections in your database. If you need help adding your email connection, you may refer to our article here: Adding Email Connection.
We also have an article describing what a Shared Email Connection is as well.
When navigating to your 'my settings & preferences' area, you'll notice in the screen shot below, there are 2 email connections. The connection with the highlighted yellow star will be your primary connection. To change this, simply select the non-highlighted star. After making this change, you'll want to save and refresh your browser.
If you simply wish to send from a different email but do no wish to change your primary email connection, you may select your email address before attempting to send. This will pull a drop down menu below displaying all email connections that you have created or that have been shared in your organization.