Amazon Simple Email Service
Developer Guide

Email Program Success Metrics

There are several metrics that help measure the success of your email program. This section provides information about the following metrics:

Bounce Rate

A bounce occurs when an email cannot be delivered to the intended recipient. There are two types of bounces: hard bounces and soft bounces. A hard bounce occurs when the email cannot be delivered because of a persistent issue, such as when an email address does not exist. A soft bounce, occurs when a temporary issue prevents the delivery of an email. Soft bounces can occur when a recipient's inbox is full, or when the receiving server is temporarily unavailable. Amazon Simple Email Service handles soft bounces by attempting to redeliver soft bounced emails for a certain period of time.

It is essential that you monitor the number of hard bounces in your email program, and that you remove hard-bouncing email addresses from your recipient lists. When email receivers detect a high rate of hard bounces, they assume that you don't know your recipients well. As a result, a high hard bounce rate can negatively impact the deliverability of your email messages.

The following guidelines help you avoid bounces and improve your sender reputation:

  • Try to keep your hard bounce rate below 5%. The fewer hard bounces in your email program, the more likely ISPs will see your messages as legitimate and valuable. This rate should be considered a reasonable and attainable goal, but is not a universal rule across all ISPs.

  • Never rent or buy email lists. These lists may contain large numbers of invalid addresses, which could cause your hard bounce rates to increase dramatically. Furthermore, these lists could contain spam traps—email addresses specifically used to catch illegitimate senders. If your messages land in a spam trap, your delivery rates and sender reputation could be irrevocably damaged.

  • Keep your list up to date. If you haven't emailed your recipients in a long time, try to validate your customers' statuses through some other means (such as website login activity or purchase history).

  • If you don't have a method of verifying your customers' statuses, consider sending a win-back email. A typical win-back email mentions that you haven't heard from the customer in a while, and encourages the customer to confirm that they still want to receive your email. After sending a win-back email, purge all of the recipients who did not respond from your lists.

When you receive bounces, it is vital that you respond to them appropriately by observing the following rules:

  • If an email address hard bounces, immediately remove that address from your lists. Do not attempt to re-send messages to hard-bouncing addresses. Repeated hard bounces add up, and ultimately harm your reputation with the recipient's ISP.

  • Make sure that your bounce submission address is itself capable of receiving emails.

  • If your inbound email comes to you from an ISP, instead of through your own internal servers, an influx of bounce notifications can land in your spam folder or be dropped completely. Ideally, you should not use a hosted email address to receive bounces. If you must, however, then check the spam folder often, and don’t mark the bounce messages as spam. In Amazon SES, you can specify the address to which bounces are sent.

  • Usually, a bounce provides the address of the mailbox refusing delivery. However, if you need more granular data to map a recipient address to a particular email campaign, include an X-header with a value you can trace back to your internal tracking system. For more information, see Appendix: Header Fields.


A complaint occurs when an email recipient clicks the "Mark as Spam" (or equivalent) button in their web-based email client. If you accumulate a large number of these complaints, the ISP assumes that you are sending spam. This has a negative impact on your deliverability rate and sender reputation. Some, but not all, ISPs will notify you when a complaint is reported; this is known as a feedback loop. Amazon SES automatically forwards complaints from ISPs that offer feedback loops to you.

The following guidelines help you avoid complaints and improve your sender reputation:

  • Try to keep your complaint rate below 0.1%. The fewer complaints in your email program, the more likely ISPs will see your messages as legitimate and valuable. This rate should be considered a reasonable and attainable goal, but is not a universal rule across all ISPs.

  • If a customer complains about a marketing email, you should immediately stop sending that customer marketing emails. However, if your email program also includes other types of emails (such as notification or transactional emails), it may be acceptable to continue to send those types of messages to the recipient who issued the complaint.

  • As with hard bounces, if you have a list that you haven't sent email to in a while, ensure that your recipients understand why they're receiving your messages. We recommend that you send a welcome message reminding them of who you are and why you're contacting them.

When you receive complaints, it is vital that you respond to them appropriately by observing the following rules:

  • As with bounces, make sure that your complaint submission address is itself capable of receiving emails.

  • Make sure that your complaint notifications are not being marked as spam by your ISP or mail system.

  • Complaint notifications usually contain the email content; this is different from bounce notifications, which typically only include the email headers. However, in complaint notifications, the email address of the recipient who complained is typically removed. Use custom X-headers or special identifiers embedded in the email body so that you can identify the email address that filed the complaint. This technique enables you to remove the address from your recipient lists.

Message Quality

Email receivers use content filters to detect certain attributes in your messages to identify whether your message is legitimate. These content filters automatically review the content of your messages to identify common traits of unwanted to malicious messages. Amazon Simple Email Service uses content filtering technologies to help detect and block messages that contain malware before they are sent.

If an email receiver's content filters determine that your message contains the characteristics of spam or malicious email, your message will most likely be flagged and diverted from recipients' inboxes.

Remember the following when designing your email:

  • Modern content filters are intelligent, continuously adapting and changing. They don't rely on a predefined set of rules. Third-party services such as ReturnPath or Litmus can help identify content in your email that could trigger content filters.

  • If your email contains links, check the URLs for those links against blacklists, such as those found at and

  • Avoid using link shorteners. Malicious senders may use link shorteners to hide the actual destination of the link. When ISPs notice that link shortening services—even the most reputable ones—are being used for nefarious purposes, they may blacklist those services altogether. If your email contains a link to a blacklisted link shortening service, it won't reach your customers' inboxes, and the success of your email campaign suffers.

  • Test every link in your email to ensure that it points to the intended page.

  • Make sure your website includes Privacy Policy and Terms of Use documents, and that these documents are up to date. It is a good practice to link to these documents from each email you send. Providing links to these documents demonstrates that you have nothing to hide from your customers, which can foster a relationship of trust.

  • If you plan to send high-frequency content (such as "daily deals" messages), ensure that the content of your email is different with each deployment. When you send messages with high frequency, you must ensure that those messages are timely and relevant, rather than repetitive and annoying.