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Invalid Email Address for Customer

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Last updated on Aug 20, 2026

Maxio Core's QuickBooks Sync Issues list can show the following message for a Customer record:

The email address specified for this customer is invalid.

This means a Customer that synced into Maxio Core from QuickBooks has an email address that QuickBooks does not accept, and an Invoice for that Customer is queued to sync to QuickBooks with that address attached. Until the address is corrected, new Invoices for that Customer will keep failing to sync to QuickBooks.

Why an invalid Customer email address blocks the sync

Maxio Core checks that an email address is properly formatted whenever you type one directly into a Customer or Billing Profile record. QuickBooks does not apply that same check when a Customer's email address is entered there. When a Customer syncs from QuickBooks into Maxio Core, Maxio Core writes QuickBooks's stored email address straight onto that Customer's QuickBooks Billing Profile without re-validating it, so an address QuickBooks already holds can still land in Maxio Core in an invalid format.

When Maxio Core later builds an Invoice to send to QuickBooks for that Customer, it includes the Billing Profile's email address on the Invoice if the Invoice is set to be emailed. QuickBooks then rejects the Invoice because it does not consider that address valid, which produces this error. What QuickBooks itself accepts as a valid email format is set by QuickBooks, not Maxio Core, so this check happens outside Maxio Core and cannot be changed from Maxio Core's side.

Correct the Customer's email address in QuickBooks

Because Maxio Core pulls this address from QuickBooks on every Customer sync, correcting it only in Maxio Core will not resolve the issue — the same invalid address will come back the next time the Customer syncs. Fix the address in QuickBooks instead, then let the correction sync back into Maxio Core.

To correct the invalid email address

  1. If the error message names the Customer, open that Customer's record in Maxio Core. If it doesn't, open the Invoices to Send list on your Maxio Core Home page and check each Invoice's Customer.
  2. Open the Customer and select the QuickBooks Billing Profile tab to see the email address Maxio Core currently has on file for that Customer.
  3. In QuickBooks, correct that Customer's email address.
  4. Sync your Customers so the corrected address comes into Maxio Core, then send the Invoice again.

If you have more than a few dozen Customers to check, contact support@maxio.com and Maxio Support can help you identify the Customers with bad email addresses.

Another Customer field that QuickBooks and Maxio Core can disagree on is the Customer's name; see Customer Name Mismatch with QuickBooks for how that mismatch appears and how to resolve it.

A similar sync failure can happen because of the Invoice's address instead of the Customer's email address; see QuickBooks Sync Issue: A suitable address could not be found for this Invoice for that case.

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