If emails aren't sending to customers, you will want to check a few places to make sure your email settings are enabled.
The first place to look is the company-wide email settings: settings->company->summary.
The next thing you will want to check is if you have your email notifications set to only send to people with a verified email address. If this box is checked, people who haven't verified their email won't get emails, even if it is a good email. Settings->configuration->email notifications.
If customers still aren't receiving their client agreements, first check the company-wide welcome email notifications and make sure this box is checked.
If a customer is still not receiving their agreement / welcome email, you might want to check the agreement settings. If this box is checked, it won't automatically send the welcome email for this particular agreement.
If after all this, the customer still isn't receiving emails, there are two more places to check:
You can check that under an individual customer's profile by going to their history->emails or by going to the company-wide email report by going to reports->history->emails. The status column in these reports will show you whether the emails are going through or not. If the status is sent or delivered, they are getting their emails but not opening them. If it says "clicked," they opened the email and clicked on a link. If it shows "bounced" or "hard bounced," it is either a bad email (entered incorrectly) or your emails are blocked.
2. The customer's email settings
