Are 550 5.7.1 and 554 classified as hard bounces?

Yes, both 550 5.7.1 and 554 are considered hard bounces. A hard bounce indicates a permanent delivery failure, meaning the email will never be successfully delivered to that specific recipient address. Continuing to send to addresses that generate hard bounces can negatively impact your sender reputation over time.

What's the main difference between a 550 5.7.1 and a 554 error?

The key difference lies in specificity. While both indicate permanent rejections, 550 5.7.1 often points to specific security or policy violations, such as being on a blocklist or being flagged as unsolicited mail. 554 is more generic, signifying a general permanent failure due to security policies, relay access issues, or broad content rejection. Always check the accompanying text for more context.

What are the first steps to troubleshoot these bounce errors?

Start by examining the full bounce message for specific details. Then, check your sending IP and domain against public blocklists. Ensure your SPF, DKIM, and DMARC records are correctly configured. Review your email content for anything that might trigger spam filters. If you use an ESP, particularly with a shared IP, contact them for deeper insights and assistance.

Does sender reputation affect whether I get 550 or 554 errors?

Yes, sender reputation plays a significant role. If your IP address or domain has a poor reputation, or if it's been listed on a blocklist (or blacklist), recipient servers are more likely to reject your emails with these error codes. Maintaining good sending practices and monitoring your reputation are crucial.

How do email authentication protocols relate to these bounce messages?

Authentication failures, particularly with SPF, DKIM, and DMARC, are a common cause. When recipient servers cannot verify that your email is legitimately from your domain, they are likely to reject it to prevent spoofing and spam. Ensuring these records are correctly set up and aligned is vital.

What do bounce error messages 550 5.7.1 and 554 mean and how to resolve them? - Troubleshooting - Email deliverability - Knowledge base

Email bounce messages are an unavoidable part of sending emails. While some are temporary, others, like the 550 5.7.1 and 554 errors, indicate a permanent problem. These permanent (hard) bounces mean the email will not be delivered, and further attempts to send to the same recipient without addressing the root cause will also fail, potentially harming your sender reputation.

Understanding these specific SMTP error codes is crucial for effective email deliverability. They typically point to issues related to security policies, sender reputation, or content. While the codes themselves provide a general category, the accompanying text offers more specific clues about why your message was rejected. Often, they indicate that the receiving server simply does not want your mail, for various reasons.

Understanding 550 5.7.1 bounce errors

The 550 5.7.1 bounce error is a common permanent delivery failure indicating that the message was rejected due to a security or policy issue on the receiving server's side. It's often accompanied by messages like 'unsolicited mail,' 'client blocked from sending,' or 'message rejected due to local policy.' This error implies that the recipient's system, or the Internet Service Provider (ISP) managing it, has flagged your email or sending infrastructure as suspicious or non-compliant.

A frequent cause of the 550 5.7.1 error is your sending IP address or domain appearing on a blocklist (or blacklist). ISPs, particularly large ones like

Microsoft Outlook, maintain their own internal blocklists, or subscribe to public ones, to filter out spam. If your IP or domain is listed, any mail from it will be rejected. You can find more information about how Microsoft handles error 550 5.7.1 in their documentation.

Another primary reason is a failure in email authentication protocols, specifically SPF, DKIM, and DMARC. If your emails are not properly authenticated, recipient servers may deem them illegitimate or potentially spoofed, leading to rejection. This is particularly true with new stringent requirements from major mailbox providers.

Sometimes, the content of your email itself can trigger a 550 5.7.1 error. This happens if the message contains elements commonly associated with spam, such as suspicious links, unusual formatting, or spammy keywords. The receiving server's content filters might block the message outright based on these characteristics. For example,

Gmail frequently flags emails as 'likely unsolicited mail' with this error code. You can learn more about this specific Gmail bounce by reading our article on what caused the Gmail bounce error 550-5.7.1.

Understanding 554 bounce errors

The 554 bounce error is a generic permanent failure code. Unlike 550 5.7.1, which often specifies a security or policy violation, 554 usually indicates a general permanent problem that led to the email being rejected. Common accompanying messages include 'relay access denied,' 'message rejected due to security policies,' or 'sender denied.' It's a definitive statement from the receiving server that the message will not be accepted.

One common scenario for a 554 error is 'relay access denied.' This typically means your mail server (or ESP's server) is not authorized to send mail through the recipient's mail server. This often points to an authentication issue or a misconfiguration on either the sender's or recipient's side, preventing the mail from being relayed correctly. This is distinct from a 550 relaying denied error, but carries similar implications regarding access.

Another frequent reason for 554 errors is that the message was rejected due to the recipient's security policies. This can be broad, covering anything from a local blocklist maintained by the recipient's email provider, to content-based filtering that identifies the email as spam. For instance,

Mimecast often returns 554 errors due to security policies. This suggests a proactive filtering system is at play.

In some cases, 554 errors can also be a result of detected spam content within the message, similar to 550 5.7.1 errors. The crucial difference is that while 550 5.7.1 often gives a hint about the specific security or unsolicited nature of the mail, 554 is more of a catch-all for permanent rejections based on policy or perceived abuse. Regardless of the specific error code, both 550 and 554 are hard bounces that require intervention to resolve.

Diagnosing and resolving 550 5.7.1 and 554 errors

Resolving 550 5.7.1 and 554 bounce errors requires a systematic approach. The first step is always to carefully examine the full bounce message. While the 550 or 554 code is a general indicator, the accompanying text often provides crucial details or even links to troubleshooting pages from the recipient's mail provider. This additional context can help pinpoint the exact reason for the rejection, such as a specific blocklist, a content violation, or a policy breach. Once you've identified the specific problem, you can proceed with targeted solutions.

Sender-side issues

Many 550 and 554 errors stem from problems with your sending setup or practices. Addressing these issues proactively can significantly improve your deliverability.

Sender Reputation: Check if your sending IP address or domain is on any public blocklists. If you are on a shared IP, contact your Email Service Provider (ESP) to investigate, as the issue may be with other users on that IP. They will have access to more detailed data and logs.
Authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured. These protocols verify your email's legitimacy and are critical for avoiding rejections, especially by major mailbox providers. In particular, review your DKIM setup if you suspect authentication is the issue.
Content Quality: Review your email content for anything that might trigger spam filters, such as excessive links, suspicious attachments, or overly promotional language. Consider if the email could be perceived as 'unsolicited mail.'

Recipient-side issues

Sometimes, the problem lies with the recipient's email system or address. These issues require investigation, potentially involving the recipient or their IT team.

Recipient Address: While 550/554 typically indicate policy, sometimes an underlying sub-code might point to an invalid recipient address. Double-check the email address for typos. If the address is legitimate, the issue is likely a policy or security block rather than an invalid address.
Recipient Policies: If the bounce message mentions 'security policies' or 'local policy,' it means the recipient's mail server has specific rules blocking your email. This might involve their internal blocklist (blacklist) or advanced content filtering. Contacting the recipient (via an alternative method) to have them whitelist your sending domain or IP can resolve this.
Firewall/Network Issues: In rare cases, network or firewall configurations on the recipient's side might be blocking your mail server. This would typically require the recipient's IT team to investigate their network setup and allow your mail server's IP address.

Always keep an eye on your overall deliverability. Consistent monitoring of your sender reputation, including blocklist (or blacklist) status, and authentication records, is key to preventing these types of hard bounces. Regular review of your email campaigns for content that could trigger spam filters also helps maintain a healthy sending reputation. If you're experiencing a high volume of these errors, it may indicate a broader issue with your email program or a compromise of your sending infrastructure.

Views from the trenches

Best practices

Maintain clean email lists by removing bounced addresses to protect your sender reputation.

Regularly monitor your domain and IP address against major email blocklists.

Always ensure your SPF, DKIM, and DMARC records are correctly configured and aligned.

Segment your email sends to avoid sending large volumes to unengaged recipients.

Monitor email performance through Postmaster Tools for feedback loop data.

Common pitfalls

Ignoring bounce messages and continuing to send to problematic addresses.

Failing to update or incorrectly configuring SPF, DKIM, or DMARC records.

Sending emails with generic or spammy content that triggers filters.

Relying solely on shared IP addresses without understanding their impact on deliverability.

Not engaging with your ESP for deeper insights into bounce reasons.

Expert tips

Implement DMARC with a monitoring policy (p=none) to gain visibility into authentication failures.

For shared IP issues, ask your ESP about migrating to a dedicated IP if volume justifies it.

Use email testing tools before major sends to catch content or authentication issues.

Engage with recipient postmasters directly if a domain consistently blocks your emails.

Review your sending frequency and volume to avoid sudden spikes that trigger spam filters.

Expert view

Expert from Email Geeks says these errors at first glance look like reputation blocking or spam.

2023-07-24 - Email Geeks

Expert view

Expert from Email Geeks says the 550 5.7.1 message indicates a blocklist issue, while the 554 suggests either a local blocklist or a content-based block.

2023-07-24 - Email Geeks

Keeping your emails out of the spam folder

Encountering 550 5.7.1 and 554 bounce errors is a clear signal that your emails are being rejected for persistent reasons, often related to security, policy, or sender reputation. These aren't temporary glitches, but indicators that demand immediate attention to protect your email program's health. By understanding the nuances of each error code and the context provided in the bounce message, you can effectively diagnose and address the underlying issues.

Prioritizing strong email authentication, maintaining a clean sending reputation, and crafting high-quality content are fundamental to avoiding these errors. When they do occur, leveraging the information in the bounce message and collaborating with your ESP, especially when on shared IPs, is crucial. Proactive monitoring and adherence to best practices will help ensure your messages reach their intended inboxes, fostering trust and engagement with your recipients.