There is an easy fix to this problem and I am yet to see a WSO seller utilize it. It is the Auto Responder feature in your cPanel! What this does is send out an auto reply email with a set response to any email that comes in to a specific email account.
This is a quick run down on how to set up an auto response message:
1. Log into cPanel.
2. Scroll down to the Mail section and click on the Auto Responder icon.
3. On the new page, click the Add Auto Responder button.
4. Add the appropriate information in the fields.
a) Use utf-8 character set unless you have a reason not to5. Click Create/Modify button.
b) Change interval to how many hours you want
c) Select the email address and the domain the email response will come from
d) Add who the email will be from
e) Add a subject line
f) Choose whether you want to use HTML or not
g) Add the body of your email
h) Select Start & Stop times
Now when someone sends an email to that email account they will receive that response within a few minutes. They will not be left waiting on you knowing that you will get back to them like you have promised.
I have included a screenshot for clarification.