Email Error Messages

You may be getting an error message to give you a clue as to why your email is failing.

Here are a number of failed error messages and what they might mean:

1. Server Error: Relay Access Denied 554 5.7.1

What it means
This occurs for two main reasons. The first reason is that your outgoing mail server (SMTP) doesn't allow to send emails without user authentication and the other reason is that your email address is marked at spam lists as a source of spam.

Solution
Contact us for help.

2. 554 5.7.1 recipient address was suppressed due to customer policy

What it means
It could mean that this email address has failed before or that the person on the other end of that particular email address has resulted in one of a few different actions:

• The address was invalid (address does not exist)
• The user clicked the list-unsubscribe header
• The user clicked one of your emails and flagged it as SPAM. This will add this address to your suppression List

Solution
Click here for more info on what to do (see Step 2).

3. 451 4.3.0 [internal] Sending IP temporarily suspended

What it means
These delays are due to the Adaptive Email Delivery (AEN) doing it’s job. The AEN is an integral part of SparkPost that moderates traffic to comply with ISP/server rules and feedback. When we get push back from them, our software detects these bounces and takes the appropriate action to "back off" of the receiving endpoint. Listening to feedback from ISPs allow us to stay on good terms and build a better reputation, resulting in higher deliverability for everyone on the platform.
ISPs or recipient MTAs delay messages for multiple reasons such as mail server busy or over loaded at the time of send, etc. Like other Delays, they are retried until delivered or timing out after 72 hours.
The AEN is only acting on the behavior of the ISP and is meant to hold onto your message until the ISP is able to accept it rather than receiving a block bounce and not delivering at all. It works on the concept of better late than never.
More info is here: https://www.sparkpost.com/docs/faq/understanding-delays-bounces/

Solution
The '...temporarily...' is the key here - according to the docs it means our sending system has been told to 'slow down'! So it's doing so whilst the receiving server (e.g. gmail.com) is busy or something similar. Our systems will retry when its the right time to do so.

4. Bounces (aka Permanent Failures or 5xx Errors)

What it means
When we receive a 5xx response from the ISP, we will log a "bounce" event and determine the bounce classification based on the 5xx response string. (Bounces classified as "hard" bounces (code 10) are added to the suppression list.)

Solution
Check with the contact if they are having problems with their email.