If you're the sender of a message that's getting this error, see: Getting "Hop Count Exceeded" bounce error when sending to SpamHero user
This article provides a workaround for dealing with this common Microsoft 365 bounce error:
554 5.4.14Hop count exceeded - possible mail loop
This is most commonly cause caused by a known Microsoft 365 / Office 365 design flaw that has been around for years.
The underlying problem is that Microsoft 365 sometimes accepts an inbound message and then instead of delivering to the local recipient, treats it as an outbound message. As a result, the message is relayed back to SpamHero, where it is processed and re-delivered to Microsoft (causing a loop until the message bounces).
In a hurry to get a specific message delivered?
The fastest way to get an individual message delivered when you encounter this error is to requeue it to an external email address that is not handled by Microsoft (such as a Gmail address). The following article provides the steps for delivering a message to an alternate address:
Can I re-deliver a message to an alternate email address?
Since this is caused by a bug inside of Microsoft's network, the workaround options are somewhat limited. However, through testing, we have identified a per-recipient address solution that works. The workaround is to deliver messages via the affected recipient's
onMicrosoft.com fallback domain. In most cases, the alias address already exists.
Most email users should already have a "fallback" email alias address that ends with
[yourSubDomain].onmicrosoft.com (the sub-domain is usually based on your company name or your primary domain name). Use the following steps to find the fallback email alias address for your user:
In the SpamHero control panel, you'll be updating the affected recipient so that mail is forwarded to the
onMicrosoft.com "fallback" email alias address.
onmicrosoft.com fallback alias address, as found in the Microsoft 365 admin center
I understand... checkbox
Allow a minute for the back end to process the update before re-queuing the message for delivery.
You can re-queue messages that failed to deliver because of this error. Keep in mind that because the message was looping, several duplicate copies will appear in your message viewer. Only one copy of each message needs to be released. It's also advisable to re-queue a single message first to confirm that the looping issue has been resolved.
The message should be delivered to your in-box within a minute. Other messages from senders that are affected by the Microsoft 365 mail loop bug should deliver without further changes.