Should I retry sending emails after receiving a "Connection Error" bounce reason?
Michael Ko
Co-founder & CEO, Suped
Published 20 May 2025
Updated 17 Aug 2025
8 min read
Receiving a "Connection Error" bounce reason can be frustrating, especially when you're trying to ensure your emails reach their intended recipients. It often leaves senders wondering whether to retry or if doing so could harm their email program. I frequently see questions about this, as it's a common bounce type that isn't always straightforward.
While a connection error sounds like a simple network glitch, its implications for your email deliverability can be more complex than they appear. The decision to retry depends heavily on the underlying cause, and understanding this distinction is crucial for maintaining a healthy sender reputation and achieving good inbox placement. Let's delve into why these errors occur and the best practices for managing them.
Understanding "Connection Error" bounces
A "Connection Error" bounce typically indicates that the sending server could not establish a connection with the recipient's mail server. This can happen at various stages of the SMTP (Simple Mail Transfer Protocol) handshake, preventing the email from even being fully handed over for delivery. It's often categorized as a soft bounce, implying a temporary issue that might resolve itself.
However, the term "connection error" can sometimes be a generic message for different underlying problems. It might genuinely be a transient network issue, a recipient server being temporarily offline, or an overloaded server. In these cases, a retry mechanism is usually effective, as the issue is likely to clear up quickly. You can learn more about troubleshooting connection timeout errors for messages.
On the other hand, a "connection error" can sometimes be a deliberate, though disguised, rejection by the recipient's server. This happens when a mail server actively refuses the connection without providing a specific SMTP error code like 550. This can occur if your sending IP or domain is on a blacklist (or blocklist), or if the recipient's security measures are particularly strict. Sometimes, it can even be a specific tenant-level block, especially with large email providers.
When to retry and when not to
The decision to retry emails after a connection error is nuanced. For true transient issues, retrying is not only acceptable but necessary to ensure delivery. Most email service providers (ESPs) have built-in retry mechanisms for soft bounces, gradually increasing the delay between attempts.
However, if the "connection error" is a disguised block, repeated retries can be detrimental. Continuously attempting to send to an actively rejecting server signals poor sending practices to other ISPs, potentially harming your overall domain reputation. This can lead to your emails being flagged as spam, even by recipient servers that previously accepted your mail.
The key is distinguishing between a temporary hiccup and a firm rejection. For example, if you're getting a connection error from Adobe Campaign or similar platforms, investigate the specific delivery failure reasons listed. Understanding typical email error messages can guide your retry strategy.
Good retry scenarios
These are generally safe to retry:
Temporary server issues: The recipient's mail server is temporarily down, restarting, or undergoing maintenance.
Network glitches: Intermittent connectivity problems between your server and theirs.
Server overload: The recipient's server is busy and temporarily cannot accept new connections.
If you're unsure, checking the exact bounce message or diagnostic code from your ESP can provide more clarity. Some providers, like Microsoft 365, offer mail flow intelligence that can help diagnose the issue more accurately. If you repeatedly get connection errors to the same domain without any other clear indication, it is best to suppress that address after a few retries.
Impact on sender reputation and deliverability
Continuous attempts to deliver emails to addresses that consistently return "Connection Error" bounces, especially when it's a disguised block, can severely impact your sender reputation. Internet Service Providers (ISPs) and mailbox providers (MBPs) monitor your sending patterns very closely. They look for signs of responsible sending behavior.
If your mail servers repeatedly try to connect to a domain that is actively refusing the connection, it suggests that you are either sending to invalid or unresponsive addresses, or that your sending practices are unwanted. This can lead to a lower sender score, which means your legitimate emails are more likely to land in the spam folder or be blocked entirely. For more information on this, check out our guide on understanding email domain reputation.
Beyond deliverability issues, excessive retries consume valuable resources and can inflate your bounce rates unnecessarily. While individual connection errors are typically soft bounces, a high volume of them can signal deeper issues with your mailing list hygiene. This can trigger blocklist (or blacklist) listings for your IP address or domain.
Risks of aggressive retry strategies
Aggressively retrying emails that result in connection errors, particularly when the underlying cause is a block, can have several negative consequences for your email program:
Damaged sender reputation: ISPs perceive repeated failed attempts as a sign of spamming or poor list management.
Lower inbox placement: Even if not blocked, your emails may consistently land in the spam folder.
Wasted resources: Sending attempts consume bandwidth and processing power without yielding results.
It's important to differentiate between a truly temporary connection error and one that's a signal of a more persistent issue, like a block. If you're seeing a high volume of "connection errors," it might be time to investigate your email deliverability issues more deeply. Regular monitoring of your bounce logs and reputation metrics is critical.
Best practices for handling connection errors
The most effective way to handle connection errors is to implement an adaptive retry strategy coupled with robust list hygiene. Your sending platform should attempt retries with increasing intervals for a reasonable period, typically 24-72 hours. However, if the error persists for a particular recipient beyond that, it's often best to suppress that address.
Monitoring your bounce reports closely is key to identifying patterns. Are the connection errors specific to certain domains or recipients? Is there an underlying SMTP error code that provides more detail, even if the primary message is "connection error"? For example, a 421 or 451 code suggests a temporary issue that is often retriable.
Additionally, ensuring your email authentication protocols like DMARC, SPF, and DKIM are correctly configured can reduce the chances of your emails being implicitly blocked, thereby appearing as connection errors. Strong authentication signals legitimacy to receiving servers.
Example of adaptive retry logic (pseudo-code)javascript
function sendEmailWithRetry(emailData, retries = 0) {
if (retries >= MAX_RETRIES) {
console.log(`Max retries reached for ${emailData.recipient}. Suppressing.`);
suppressAddress(emailData.recipient);
return;
}
try {
const response = sendEmail(emailData);
if (response.status === 'success') {
console.log(`Email sent successfully to ${emailData.recipient}.`);
} else if (response.bounceReason === 'Connection Error') {
const delay = Math.pow(2, retries) * 1000; // Exponential backoff
console.log(`Connection error for ${emailData.recipient}. Retrying in ${delay / 1000} seconds.`);
setTimeout(() => sendEmailWithRetry(emailData, retries + 1), delay);
} else {
console.log(`Permanent bounce for ${emailData.recipient}. Suppressing.`);
suppressAddress(emailData.recipient);
}
} catch (error) {
console.error(`Error sending email to ${emailData.recipient}: ${error.message}`);
const delay = Math.pow(2, retries) * 1000;
setTimeout(() => sendEmailWithRetry(emailData, retries + 1), delay);
}
}
For ongoing issues, consider using SparkPost's bounce event data or similar analytics to dig into the specifics. Sometimes, the problem lies with a specific mail exchange (MX) record or an issue on the recipient's DNS side, which might require their intervention.
Retry strategy
Description
Impact on deliverability
Immediate retry
Attempt to resend the email within seconds of the initial failure.
Useful for fleeting network glitches, but risky if the server is intentionally rejecting connections. Can look spammy if overused.
Fixed interval retry
Resend after a set time, e.g., every 15 minutes, up to a limit.
Better than immediate, but doesn't adapt to server load. Still risks reputation if the issue is a block.
Exponential backoff
Increase delay between retries exponentially, e.g., 1 min, 2 min, 4 min.
Recommended for most soft bounces. Reduces load on recipient servers and appears more polite, safeguarding reputation.
Adaptive suppression
Stop retrying and suppress the address after a fixed number of failures or a defined period.
Crucial for protecting sender reputation against persistent blocks or invalid addresses masquerading as temporary errors. Improves list hygiene.
Ultimately, the best approach is to treat "Connection Error" bounces as soft bounces that require an intelligent retry policy. However, be prepared to convert them to permanent suppressions if they persist, as this protects your sender reputation and keeps your email list clean. You can also explore how many retries to send to Yahoo after temporary errors for more specific guidance.
Navigating connection errors for better email health
Navigating "Connection Error" bounces requires a discerning eye and a proactive strategy. While these errors are often temporary and warrant a retry, it's vital to recognize when they are indicative of a deeper issue, such as an active block or a consistently unresponsive server. Blindly retrying can do more harm than good to your sender reputation and deliverability.
By implementing adaptive retry policies, diligently monitoring bounce reports for patterns, and maintaining excellent list hygiene, you can effectively manage these errors. Prioritizing the health of your email program ensures that your messages reach their intended inboxes, fostering better engagement and preventing your domain from being flagged as undesirable. Always remember that good deliverability is built on trust and responsible sending practices.
Views from the trenches
Best practices
Closely examine bounce message details, as "connection error" can mask deeper issues like active blocks.
Implement adaptive retry mechanisms with increasing delays and a defined maximum number of attempts.
Proactively suppress email addresses that consistently generate connection errors over a short period.
Maintain robust email authentication records, including SPF, DKIM, and DMARC, to bolster sender reputation.
Common pitfalls
Blindly retrying all "connection error" bounces without analyzing the underlying cause, leading to reputation damage.
Failing to identify and remove recipients that are actively blocking your sending domain.
Neglecting to monitor your domain and IP on email blocklists (or blacklists) after observing connection errors.
Ignoring consistent "connection errors" as merely transient issues, when they might signify deeper deliverability problems.
Expert tips
Use granular bounce analytics to differentiate between temporary network glitches and active ISP or domain-level blocks.
Segment your email lists and adjust retry policies for different segments based on historical bounce data.
Engage with postmasters of domains where you frequently encounter connection errors to understand their specific policies.
Regularly audit your sending infrastructure and network configurations to rule out your own side as the source of connection issues.
Expert view
Expert from Email Geeks says that a 'connection error' can often be a disguised active block, indicating existing domain health issues.
2024-05-20 - Email Geeks
Expert view
Expert from Email Geeks says there is no benefit in retrying emails that result in a connection error if it's an Office 365 tenant block.
Microsoft 365, offer mail flow intelligence that can help diagnose the issue more accurately. If you repeatedly get connection errors to the same domain without any other clear indication, it is best to suppress that address after a few retries.
