If you're a Gmail user, it may be because SimplePractice emails are being filtered into your Promotions tab instead of your Primary tab:
To change this, simply drag the email from the Promotions tab into your Primary tab to teach Gmail that SimplePractice messages are important to you:
Then confirm that you want to make this change:
If you're an AOL, Hotmail, or Yahoo user,
it may be because SimplePractice emails are being directed to your Junk folder. These email clients have been known to have very aggressive spam filters that catch a lot of useful messages too.
To fix this, find the SimplePractice email in your Junk/Spam folder and click the button in your email client that indicates SimplePractice emails are not spam.