Why do AWS SES emails get stuck in Send status and how can this be investigated?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Jun 2025
Updated 19 Aug 2025
8 min read
It can be perplexing when you're sending emails through AWS Simple Email Service (SES) and a significant portion of your messages seem to get stuck in a 'Send' status, never progressing to 'Delivery' or 'Bounce'. This situation is particularly frustrating during large sendouts, where 20-30% of emails remain in this ambiguous state, leaving you wondering what is actually happening to them.
The official documentation for Amazon SES monitoring describes the 'Send' event as a successful request for SES to attempt delivery to the recipient's mail server. Crucially, it notes that if account-level or global suppression is active, SES still counts it as a 'Send' even if delivery is suppressed. This nuance is often overlooked, leading to confusion when expecting a delivery or bounce event that never arrives.
The problem suggests that emails accepted by SES are not being processed further for a variety of reasons. While transient errors like DNS SERVFAIL, network outages, or temporary deferrals (4xx responses) from recipient mail servers can cause delays, the sheer volume of emails stuck in 'Send' status points to a more systemic issue.
Understanding why your emails are in this limbo is crucial for maintaining good email deliverability and ensuring your messages reach their intended recipients. It often comes down to a few key areas that require in-depth investigation. Knowing where to look for clues can help you quickly diagnose and resolve the underlying issues, preventing future messages from getting lost in the 'Send' status.
Deciphering the send status
When an email is successfully accepted by AWS SES, it transitions to the 'Send' status. This indicates that SES has taken responsibility for the message and will attempt to deliver it. However, 'Send' doesn't mean 'Delivered'. It means the email is in the queue for delivery or has been processed for sending, but the final outcome is still pending or, in some cases, intentionally prevented.
A key factor that can keep emails seemingly stuck in 'Send' is suppression lists. AWS SES maintains a global suppression list of email addresses that have recently caused a hard bounce or complaint for any SES sender. If you attempt to send an email to an address on this list, SES will accept the message (registering it as a 'Send' event) but will then suppress the delivery. This is a protective measure to preserve the sender's reputation.
Beyond the global suppression list, individual accounts can also use their own account-level suppression lists. If you've accumulated a large number of bounces or complaints historically, it's possible that many of your recipients are on either of these lists. This explains why emails might register as 'Send' but never reach the recipient, as delivery is explicitly prevented by AWS itself.
Common culprits behind stuck emails
The primary culprit for emails getting stuck in 'Send' status, especially in large volumes, is often related to suppression. As mentioned, AWS SES (and many other Email Service Providers, or ESPs) employs suppression lists to protect sender reputation. If an email address has previously hard bounced or marked an email as spam, it's added to these lists.
Beyond suppression, other factors can contribute to emails remaining in 'Send'. These often involve transient issues that delay but don't immediately fail delivery. However, if these delays persist without resolution, the emails might effectively become 'stuck' from your perspective, never reaching a clear 'Delivery' or 'Bounce' state in your monitoring.
These types of issues can be challenging to diagnose without deep insight into the email's journey post-'Send' acceptance. Sometimes, the problem lies not with SES itself, but with the recipient's mail server or intermediate network conditions. It highlights the importance of thorough monitoring and understanding what SES means by 'Send'.
Investigating and resolving issues
The first step in investigating stuck emails is to check AWS SESDeliveryDelay events. While you might not see a large number of these, they can offer clues about temporary recipient-side issues, such as full inboxes (e.g., Gmail inboxes). Ensure your event filtering isn't inadvertently hiding these events.
However, the most promising area for investigation for high volumes of 'Send' status emails is the suppression list. AWS SES has both a global and an account-level suppression list. A significant percentage of emails stuck in 'Send' strongly suggests that these addresses are on one of these lists, preventing actual delivery. You can manage your account's suppression list and even choose to disable the global suppression list to manage it yourself, though this shifts the responsibility for bounce handling to you.
Conduct a thorough review of your current suppression lists within the AWS SES console. This will help you identify if a large portion of your mailing list is being suppressed without clear visibility into why it is happening. You might find that addresses added due to past deliverability issues are still on the list, even if your sender reputation has since improved. This proactive check can reveal many of the unseen reasons for emails stuck in 'Send' status, allowing you to take corrective action, like removing suppressed email addresses.
Proactive strategies for healthier sends
To prevent emails from getting stuck in 'Send' status, focusing on list hygiene and sender reputation is paramount. Regularly cleaning your email lists to remove invalid, inactive, or bouncing addresses will significantly reduce the chances of encountering suppression issues, whether global or account-level. Implement robust bounce and complaint handling mechanisms to automatically remove problematic addresses from your active mailing lists.
Monitoring your email deliverability metrics is also critical. Pay close attention to your bounce rates, complaint rates, and overall inbox placement. High rates in any of these categories can indicate underlying issues that might lead to SES suppressing your sends. Tools and dashboards provided by SES itself, or third-party deliverability platforms, can provide the insights needed to identify and address these issues proactively. For instance, understanding troubleshooting a sudden drop in email delivery rates will help.
Additionally, ensuring your email authentication records (like SPF, DKIM, and DMARC) are correctly configured can bolster your sender reputation and prevent your emails from being flagged by recipient servers. Proper configuration of these records is a fundamental aspect of email deliverability, helping you avoid many common issues that lead to emails getting stuck or even blocked by blacklists.
Addressing the 'send' status
Emails stuck in 'Send' status with AWS SES are typically a symptom of underlying deliverability challenges, most commonly related to suppression lists. While SES signals acceptance, the actual delivery may be halted due to recipients on a global or account-specific blacklist (also known as blocklist).
Effective investigation involves checking DeliveryDelay events and, more critically, thoroughly reviewing and managing your suppression lists. Proactive measures, such as maintaining strong list hygiene, continually monitoring deliverability metrics, and ensuring proper email authentication, are vital to prevent such issues.
By understanding the nuances of SES event statuses and implementing best practices, you can significantly improve your email deliverability, ensuring your messages reliably reach the inbox rather than getting caught in a perpetual 'Send' state. This approach will also help you address why emails are not delivered.
Views from the trenches
Best practices
Maintain pristine email lists by regularly removing bounces and inactive addresses to prevent suppression.
Utilize Amazon SES event publishing to log and analyze delivery, bounce, and complaint events for actionable insights.
Common pitfalls
Ignoring high 'Send' status percentages without investigating, assuming they are normal delays.
Overlooking the impact of global or account-level suppression lists on apparent 'Send' success.
Expert tips
If migrating to account-level suppression, ensure internal bounce handling is robust.
A high percentage of 'Send' status emails without subsequent events indicates a need for list hygiene.
Marketer view
A marketer from Email Geeks says that a 'Send' event indicates that Amazon SES has accepted the email and it is queued for delivery, potentially due to transient errors or deferred responses from recipient servers.
2024-05-28 - Email Geeks
Marketer view
A marketer from Email Geeks suggests that emails stuck in 'Send' status might be due to suppression lists, which is a common practice among Email Service Providers.
AWS Simple Email Service (SES) and a significant portion of your messages seem to get stuck in a 'Send' status, never progressing to 'Delivery' or 'Bounce'. This situation is particularly frustrating during large sendouts, where 20-30% of emails remain in this ambiguous state, leaving you wondering what is actually happening to them.
Gmail inboxes). Ensure your event filtering isn't inadvertently hiding these events.
