Hey there @altearnit -- great question!

First, let’s clarify.

For some context, with Calendly, there are two types of invitee booking notifications: Email Confirmations & Calendar invitations.

1. With Email Confirmations, Calendly sends the invitee an email notification from notifications@calendly.com and has a reply-to address that's associated with your Calendly login email. You can modify this on Account Settings page.
2. With Calendar Invitations, your connected calendar sends the invitee a notification of the booked meeting which has a reply-to address that's associated with your Add to calendar email on your Calendar Connection page.

Note: Calendar invitations are not compatible with iCloud Calendar or the Outlook Plugin (for Windows users). Users with either of these calendar connections set up as their "add-to calendar" on their Calendar Connection page will be defaulted to Email Confirmations. 

Now that we’ve got a better understanding of the two types of invitee booking notifications/confirmations -- let’s dig into your question.

• You cannot set up email confirmations to be sent from the email address of the host - they will always come from notifications@calendly.com 
• That said, the reply-to email address for all email confirmations will be the login email address the host uses for Calendly
• If you choose to set up calendar invitations instead of email confirmations, those will be sent from the email address/add-to calendar of the host 

You’ll need to decide which is most important, here -- the email address the invite/confirmation is being sent from or the type of invite/confirmation being sent. If the email address is highest priority, switch all event types to “calendar invitations.” If the confirmation being an email is highest priority, keep all event types set to “email confirmations” with the understanding that they will always be sent from notifications@calendly.com with a reply-to email address of the login email address the host uses for Calendly.

I hope this helps!