Intuit programmers apparently don't now how to write a RegEx

Hi there, @larshubb.

Thanks for adding a screenshot and all the information you've provided for me to understand the situation. I'm here to help and share some insights, so you get your Invoices sent in QuickBooks for Mac.

The error message you received means that the Username and Password specified in your Preferences aren't matching the sign-in info of your email address. To resolve this, I recommend making sure your login info for your email is correct. 

Here's what you'll need to do:

1. Click the QuickBooks menu.
2. Select Preferences and click the Email icon.
3. Hit Custom in the Send Emails Using section.
4. A list of Email Accounts will appear. If you haven't added any email accounts to QuickBooks, this list will be empty.
5. Tap the + button to add a new account.
6. Add an account a name, then add the settings from your email provider.
7. Repeat for any other accounts you’d like to add.

Once done, try to send the invoice again and check to see if it works. However, if the issue persists, check the system requirements to make sure your email account is compatible with your QuickBooks version. Check out this article for more information: System Requirements.

Please let me know how it goes by leaving a comment below. I'm just a post away. Have a great day.

Well, no. Perhaps I should have stipulated that I am not an idiot.

If what you claim were the case, then none of the invoices I send out would be passed. I send out between 20 and 30 a month, and the system works fine, except in one case. It is ONLY this client, ONLY this domain, hence my observations that QB programmers don't know how to form a proper regex

Thanks - we'll investigate it. For what its worth and rather suprisingly writing a regEx to determine a valid email address is a famously difficult problem. 

https://stackoverflow.com/questions/201323/how-to-validate-an-email-address-using-a-regular-expressi...

It may not even be our code that's causing the issue - we use SendMail libraries for this function (assuming you are using the built in email option in QuickBooks Mac and not the AppleScript bridges to Apple Mail or Microsoft Outlook).

Yes, writing a regex is not simple... but isolating 'com' without taking into account the preceding period/decimal is a rookie mistake.

Sendmail -- which is what I am using, not any Applescript silliness -- does not have this problem, or it least it didn't when I owned an ISP and we ran an email cluster for thousands of users.