In the "Directory" Plugin, new subscriber emails are taking 2 hours or more to be received

This site is in the testing phase, but when I try to sign up as a user in order to set up a listing in the directory on this page:
After I click on "New Account" and enter the requested info, it says , Success you will receive an email with your password.
However, here is the problem. It is taking 2 or more hours for this email to show up. In some of the tests, it hasn't shown up at all.
Please let me know how to resolve this issue, as the person should receive the email immediately so that they can post their directory listing.
Thanks so much for your help with this issue.
Leslie Hait