Do you use appointment confirmation emails in your business? Do you feel like maybe you forget something every time you send one?
First: these emails should be automated. Your client schedules time with you. Your scheduling or email marketing software sends the confirmation almost instantly.
If any of these require more than a short paragraph or so, send in a separate email. And let the person know in the confirmation that the information is coming separately and what to look for.
How many times have you dug through your inbox trying to find an important email only to realize hours later the from name is something random like "Turner Welcome Systems" even though the company name is "Blue Enterprises."
And the subject line is something bland like "Your Confirmation."
Make your subject line clear so your readers can search for it later. This is a person who has scheduled time with you in some way. They WANT to talk to you - make it easy. For example: "Confirmed - Meeting with Amy Cocke." or "You're all set for 5 Secrets to Clearer Skin Your Dermatologist Hasn't Told You. Details inside."
You want this person's experience of working with you to be as easy as possible. Whatever makes that experience better - add it to your confirmation email or a subsequent email.