How to resolve the "Unable to reach customer email" error when sending an invoice from Quickbooks Online?

Thank you for outlining those initial troubleshooting steps, brian236. The error you're encountering is often related to the email configuration in QuickBooks Online (QBO). Let’s work through some steps to resolve this issue.

The "Unable to reach customer email" error typically means that the recipient’s firewall or email provider is flagging the Intuit domain. To resolve this, I recommend that you reach out to your customer and ask them to contact their IT expert. This expert can help add the QBO mail server hostnames and IP addresses to their outgoing mail server's allowlist. Doing so will help ensure that your QuickBooks emails are not mistakenly marked as spam.

The steps to add the hostnames and IP addresses depend on the specific email setup. You can check the list of hostnames and IP addresses that your IT expert needs to add to the allowlist in this article: Troubleshoot if customers aren't receiving emails from QuickBooks Online. Then, navigate to the Server Hostname and IP Address section for more details.

In addition, we have a team of experts who can offer personal guidance on linking your accounts, automating tasks, and teaching the best bookkeeping practices to increase your efficiency. Check out QuickBooks Live Expert Assisted for more details.

If you have further questions, let us know in the comments.