Emails and SMS are a service provided at no extra cost by Buildxact.
They are sent out of Buildxact are per user. e.g. if an account has two users - User A and User B, set up with their own email address and mobile number, if User A sends an email the "from" email address with be that of user A. And if User B sets a reminder in the schedule the "from" phone number and email will be that of user B.
A note about reminders: The "from" address and mobile number for a scheduled reminder will always default to the original creator e.g. User A creates a reminder for 2 days before, then User B opens the reminder and re-sets it to 3 days before, the "from" details will be that of user A as they originally created the reminder.
How to set up User details
Click on My Account > Users and click the Edit pencil against the user you wish to set up