Why am I seeing a spike in hard bounces later in my email campaign sends?

Email marketer from Mailchimp shares that regularly cleaning email lists is essential to remove inactive or invalid email addresses. This prevents sending to addresses that will hard bounce, thus preserving sender reputation.

Email marketer from StackOverflow explains that bounce rates will always fluctuate. A larger audience will have more drop off. You should be concerned when you suddenly see a big spike, for example > 2%

Email marketer from Neil Patel's Blog explains that hard bounces occur when an email address is invalid or doesn't exist. A sudden spike might indicate outdated email lists or changes in recipient email addresses due to job changes or account closures.

Email marketer from Validity recommends sunsetting inactive email subscribers, as a lack of engagement is a large indicator of old/abandoned addresses. Having a policy that removes subscribers from your list after a period of no engagement.

Email marketer from Reddit explains that it is normal for email lists to decay over time, resulting in more hard bounces. The longer it's been since they opted in, the higher chance they have moved companies and the email doesn't exist anymore.

Email marketer from Email on Acid states that sending emails to purchased or scraped lists almost always results in high bounce rates. Using only permission-based lists is crucial for maintaining a healthy sender reputation.

Email marketer from Litmus suggests using email validation services to proactively identify and remove invalid or risky email addresses before sending. This helps prevent hard bounces and improves deliverability.

Email marketer from HubSpot notes that using double opt-in can significantly reduce hard bounces. This practice ensures that only valid and actively consenting email addresses are added to the list.

Expert from Spam Resource explains that spikes in hard bounces can be attributed to sending to old or unengaged addresses. Over time, email addresses become inactive as people change jobs, switch ISPs, or abandon accounts.

Expert from Email Geeks suggests the observed hard bounce pattern might be due to spam filters reacting to traffic spikes. He explains that a spam filter may deliver or defer earlier emails and then start rejecting traffic once it detects the spike. Furthermore, he advises checking underlying delivery logs for confirmation.

Expert from Email Geeks suggests that the deployment method (bursts of 500/s) might look suspicious to some domains with shared backends, and/or the URN sorting pushes addresses with longer tenure to the front. He also recommends getting the SMTP Bounce Reason codes via a data view.

Expert from Word to the Wise answers that bounce rate management can involve using confirmation emails (double opt-in) to ensure recipients entered correct information and are willing to receive mail.

Expert from Email Geeks suggests getting a list of all delivery attempts to one particular domain, the timestamp they were sent, the response code, and for the failures the full rejection message and peer IP.

Expert from Spam Resource explains a less common reason for bounce rate spikes is a list bombing attack. This is when an attacker signs up a target email address for large amounts of mailing lists.

Expert from Email Geeks suggests that hard bounces take time to occur and that first benchmarks haven't had time to bounce anything, then you see bounces grow overtime.

Documentation from SendGrid Documentation defines a hard bounce as an email that cannot be delivered for permanent reasons, such as a non-existent email address or a blocked domain. Spikes in hard bounces can negatively impact sender reputation.

Documentation from Microsoft Support details SMTP response codes. A 5xx error, such as 550, indicates a permanent failure, leading to a hard bounce. It's possible your IP may be blocked if the mail is considered harmful.

Documentation from AWS Documentation explains that Amazon SES automatically handles bounces. A spike in hard bounces may trigger alerts and impact the account's sending limits if the bounce rate exceeds acceptable thresholds.

Documentation from RFC Documentation details SMTP response codes. A 5xx error, such as 550, indicates a permanent failure, leading to a hard bounce. Understanding these codes helps in diagnosing delivery issues.