main account sends invoices but other users get wrong password error

Hi there, @GeoffMohr.

I'm here to share details if QuickBooks refuses to accept your password when you use email services such as Gmail.

If you see a message about an incorrect email address or password, I've got some remedies for you.

First, we can upgrade our Account to the most recent version. Then send yourself an email with a test transaction.

Second, we can launch your email client. Investigate your filter preferences and settings. These could be accidentally blocking your QuickBooks emails.

Examine your app's preferences. Something could be interfering with your Google account connection:

1. Follow the steps to enable access to less secure apps.
2. You can also set access preferences for specific apps, like QuickBooks.
3. Go back into QuickBooks and email yourself a test transaction.

If you are still unable to send emails, disable the 2-Step Verification feature for your Gmail account.

Here's how:

1. Open your Google Account.
2. In the "Security" section, select 2-Step Verification. You might need to sign in.
3. Select Turn off.
4. A pop-up window will appear to confirm that you want to turn off 2-Step Verification. Select Turn off.

Then, we can go further to step 3 to remove passwords from apps you no longer use from this link. 

If you want to personalize your emails to customers and vendors, I've added an article: Create custom email templates in QuickBooks Desktop.

You're always welcome to comment below if you have other queries about QuickBooks. I'll be here to help if you want to create a report. Take care.