Here is the email I received back in August. I first reported this issue in January of 2024...

Hello there, dixiedoor4277. We truly value your efforts and want to reassure you that addressing your concerns is a top priority for us.

To ensure your issue is handled with the urgency it requires, I have escalated your case to our Next Level Help team. They will carefully review both your comments in the Community and your previous interactions with our support team. An expert will be in touch within the next 1-2 business days to discuss the next steps and actively work towards a resolution.

In the meantime, if you have any other issues or further questions, dixiedoor4277, please don't hesitate to reach out in the Community. We’re here and ready to assist you with anything you need.

I'm having the same issues as @dixiedoor4277  and @DamienAccounting  and they have been going on since Nov 2024. I've called every single month and now every week and they still say the case is open and they are trying to resolve it. They always give me alternate troubleshooting issues and I've literally read every post with all troubleshooting recommendations, tried them all and still we have the same problems. Now today we've been testing with our own personal emails and are not receiving emails. We have multiple that we cannot be sure are going out or not and it's so complicated now that we just need QuickBooks to resolve this issue yesterday. What is happening?! If we don't have any improvements, we're looking at cancelling our account and moving onto a different platform, we will also be asking for a refund. I can make sure my clients are getting emails eventually with manual workarounds, but this is NOT ideal long term and has our business appearing very unprofessional. 

Has anyone had any positive results with these suggestions? I've tried them all as well as the suggestions given to me over the phone and nothing is resolving this issue. If anyone has resolved this issue. Please post what worked!

I have not. I think it might be due to people Unsubscribing from QuickBooks emails. 

I've had to resort to manually emailing clients the invoice link (not ideal).

Oh goodness! Not ideal at all! I have a new open case. Hoping that here will be results this time that I can post here. Fingers crossed!

Try to get them to escalate your case to the Next Level Help Team. I finally got a sweet woman on the phone named Brittany that was able to access my account and clear the error. All emails are now being sent without error. She was able to fix this in less than 5 minutes on the phone. I asked her how to help you guys and she said you must contact QuickBooks first, and they can escalate your problem to the back office to have this fixed. So just make sure your case is escalated and they will call you. 

Took them long enough, but they do now how to fix this issue for us now.

Thank you! I do have my case escalated now. But it's not seemingly a 5 minute fix. Wondering if you know what they did that worked.

I am not sure exactly what they did on their end, but it was a super easy fix. I spoke with Brittany with the "Intuit's Advanced Escalation Team". She said your case has to be sent to her department. So maybe ask that it be escalated to that particular team? The number she called me from was 1-800-446-8848. I was on the phone with her for 8 minutes and within that time, I was able to log out, log back in and send invoices successfully. I hope you can get yours escalated!

Thank you!!!

I FINALLY GOT THIS WORKING!

when sending an invoice to a customer, there is a centerfield where you can select into it as a sender or your company email as a sender.  At some point we had added our company email as a sender.  This causes some sort of a bug in the system and into its servers have issues with sending emails with other company domains in this Sender address.  So I clicked the drop-down menu under sender and chose to delete email address, or better said the company’s email address, And only left the intuit email address as the sender.  That is the default.  Then I had to erase the last couple of characters on the customer’s email address so that it would think I was typing a new one.  Then I retype the character characters I had deleted and immediately press send.  The invoice sent without an issue anymore.  New invoices sent without a problem.  But invoices that you previously tried to send where you receive the message unable to reach, Will have to be sent in this way where you make sure that the sender is into it and that your company’s email is no longer an option as a sender, and you will have to delete the last few characters of your customer’s email address and retype them.  Do not click anything else after you retype them other than send.  If you click on anything else, you will have to erase the last few characters of the customer’s email address again before you click send.  All new invoices are sending just fine without having to erase any characters in the customer’s email address.  So again, this only applies to emails where you are sending a previously unsent invoice.  I hope this helps someone else.  And just FYI, the customer will receive the email and the from will indicate Your company‘s name at intuit.quickbooks.com, But if the customer clicks reply to the email, It will send it to whatever email you have selected as your company email in your company settings.  So you will still receive emails from your customer. Into its email address it’s only used to send the invoice to them

I got this to work! Remove company email as the sender in the sender options in the invoice.  Delete it permanently. the sender should be intuit. [email address removed] will be the option there. the customer will still reply to the email that you have setup in company settings, but the sender of the invoice will be the intuit address for your stoma

Amazing! Thank you for sharing this. Do you happen to know if there's a way to make the change to ALL invoices? We use reoccurring ones so they're all set up to go out automatically. Is there somewhere in the settings that you can change the email address all invoices are sent from? Changing every client manually is a nightmare for us. 

I removed our gmail and created a new invoice and it shows being sent from the intuit email.. still receiving the same 'unable to reach' error message. UGHHH. This is only happening with one customer. Just doesn't make any sense!

Welcome to the thread, Jennifer1102! It's wonderful to see you make your first post! I truly appreciate the information you've provided. Ensuring your invoices are successfully delivered is vital for effectively tracking your revenue data. I’m here to assist you with some troubleshooting steps to help resolve the undeliverable error message you’ve encountered, so you can manage your business smoothly and confidently.

Have you had a chance to verify your customer's email address? If you haven't already, I recommend following these steps to ensure it’s accurate:

1. Go to Customers & leads and select Customers.
2. Choose the customer you are experiencing issues with regarding invoice delivery.
3. Click Edit.
4. Check the email address and update it if needed.
5. Hit Save. 
6. Resend the invoice.

Right after, ask your customer to check their junk or spam folders if they didn't receive it in their inbox.

Next, you can clear your email address and re-enter it in your company settings to refresh the system. Here's the step-by-step guide to complete the process:

1. Go to Settings and pick Account and settings.
2. In the Company section, click Edit in Contact info.
3. Clear the Company email field and enter the desired address as is, even if it appears correct. (Note: Be sure not to use any extra characters or spaces before, within, or after the address you enter).
4. Hit Save, then Done. 
5. Send yourself a test transaction.
6. If you still don't receive the email, try using a different email address that has a different domain (for instance, if you were using a Gmail email address, try a Hotmail or Yahoo address instead).

For the comprehensive guide about the steps above, please see this article: Troubleshoot if customers aren't receiving emails from QuickBooks Online.

Moreover, would you like to enhance your customer interactions by personalizing your sales forms with specific details? If you're interested, I have some great resources to help you: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm glad I was able to assist you today, Jennifer1102. You can always return here by commenting below if you have clarifications or questions about managing your invoices and sales transactions or related topics. I'll make sure to respond as soon as possible. Wishing you productive and successful business operations!