As it's been reported several times over the past two years. Intuit servers are blacklisted. After hasving difficulties two weeks ago my hosting company, Siteground, have come back with the following information. This is 100% intuit's issue to solve. It's 100% an issue which Intuit have ignored.
Here is the proof:
Your frustration from the ongoing mail issue is understandable, so I dedicated my time to carefully go through the information that you have provided us and also analyzed our latest mail server logs.
I would like to focus the attention of this ticket conversation to you reply from '22 Feb, 2024, 03:32', where you explain in details how the Quickbooks Online service is supposed to work and how it is working after the occurrence of the problem.
From that reply I found out that order/invoice emails originate from [email address removed] to the customer's email address and are also CC-ed to your email address [email address removed].
Our mail server is rejecting these emails and only the customer email address is receiving them. When they try to reply to that email, they also receive a bounce back that [email address removed] cannot be contacted.
After some digging around, I found multiple emails from [email address removed] between 26th and 28th of February that were rejected by our incoming spam filter. As we explained earlier in this ticket, such emails are recorded with sender address like the following on our end:
bounces+2327135-e744-sales=[email address removed]
but the more important part is the sender IP address. I gathered all sender IP addresses related to Intuit. Here is a list:
159.183.100.233, 167.89.58.138, 167.89.82.233, 167.89.58.229
There is something in common about these IP addresses, they are all blacklisted in multiple global databases and you can verify that from here:
https://mxtoolbox.com/SuperTool.aspx?action=blacklist%3a167.89.58.229&run=toolpage
This is why we reject every email that originates from Intuit, as their IP ranges seem to have very poor reputation. If they manage the delist their IP ranges, the order/invoice emails should reach [email address removed] without a problem.
You might be wondering why when the customers are trying to reply to the order/invoice email, they are also unable to do that and receive a bounce back. Well this is coming from the fact that @e.notification.intuit.com remains in the headers of the email as the original sender of the email and this again triggers our incoming spam filter.
