Why does Quickbooks online keep using an old email address that I have changed when sending?

I understand that your time is valuable, Cheryl. Let me guide you through updating email addresses set for reminders.

To send invoice reminders automatically via email, we need to enable the default email message feature. This will allow you to set a default message for Reminders 1, 2, and 3, which will then be sent to the email address associated with your customers. 

Here's how: 

1. Go to the Gear icon, select Account and Settings. 
2. Locate the Sales tab, click Reminders, and toggle on the Automatic invoice reminders button.
3. Under Reminders 1, 2, and 3, you may enter a default email message you'll want to appear in the sales forms, otherwise, turn it off. 
4. Once done, click Save. 

Also, we need to take note that updating an email address will be set to the sales forms moving forward. You'll be able to send an automatic email reminder to your sales forms. 

In the meantime, you'll need to manually send reminders to your customers so that you can input the correct email address.

Here's how: 

1. Go to Sales, select Invoices.
2. Click the dropdown ▼, and then Send reminder. 
3. Edit the To or Cc/Bcc box, then input the correct email address. (Email address can be more than one. Just make sure to separate it with a comma.)
4. Once done, hit Send. 
   
   The screenshot is attached for visual reference. 

However, if the issue persists, we recommend contacting our support team. They have the necessary tools to further investigate the issue.

Do not hesitate to reply to this thread should you need additional assistance managing your sales forms. I'll keep an eye out for it. Keep safe.