Amazon SES SMTP issues - Amazon Simple Email Service
SMTP response codes

Amazon SES SMTP issues

This section contains solutions for several common issues related to sending email through the Amazon SES Simple Mail Transfer Protocol (SMTP) interface. It also contains a list of SMTP response codes that Amazon SES returns.

To learn more about sending email through the Amazon SES SMTP interface, see Using the Amazon SES SMTP interface to send email.

  • You can't connect to the Amazon SES SMTP endpoint.

    Problems connecting to the Amazon SES SMTP endpoint are most commonly related to the following issues:

    • Incorrect credentials – The credentials that you use to connect to the SMTP endpoint are different from your AWS credentials. To obtain your SMTP credentials, see Obtaining Amazon SES SMTP credentials. For more information about credentials, see Types of Amazon SES credentials.

    • Network or firewall issues – Your network might be blocking outbound connections over the port you're trying to send email from. To determine if an issue on your local network is causing connection issues, type the following command at the command line, replacing port with the port you're trying to use (typically 465, 587, 2465, or 2587): telnet email-smtp.us-west-2.amazonaws.com port

      If you are able to connect to the SMTP server using this command, and you are trying to connect to Amazon SES using TLS Wrapper or STARTTLS, complete the procedures shown in Testing your connection to the Amazon SES SMTP interface using the command line.

      If you can't connect to the Amazon SES SMTP endpoint using telnet or openssl, it indicates that something in your network (such as a firewall) is blocking outbound connections over the port you're trying to use. Work with your network administrator to diagnose and fix the problem.

  • You're sending to Amazon SES from an Amazon EC2 instance using port 25, and you're receiving timeout errors.

    Amazon EC2 restricts port 25 by default. To remove these restrictions, submit an Amazon EC2 Request to Remove Email Sending Limitations. You can also connect to Amazon SES using ports 465 or 587, neither of which is restricted.

  • Network errors are causing dropped emails.

    Ensure that your application uses retry logic when it connects to the Amazon SES SMTP endpoint, and that your application can detect and retry message delivery in case of a network error. SMTP is a verbose protocol, and sending an email using this protocol requires several network round trips. Because of the nature of SMTP, the potential for network errors increases.

  • You lose connection with the SMTP endpoint.

    Lost connections are most commonly caused by the following issues:

    • MTU size – If you receive a time-out error message, the Maximum Transmission Unit (MTU) of the network interface for the computer you're using to connect to the Amazon SES SMTP interface may be too large. To resolve this issue, set the MTU size on that computer to 1500 bytes.

      For more information about setting the MTU size on Windows, Linux, and macOS operating systems, see Queries Appear to Hang in the Client and Do Not Reach the Cluster in the Amazon Redshift Management Guide.

      For more information about setting the MTU size for an Amazon EC2 instance, see Network Maximum Transmission Unit (MTU) for Your EC2 Instance in the Amazon EC2 User Guide for Linux Instances.

    • Long-lived connections – The Amazon SES SMTP endpoint runs on a fleet of Amazon EC2 instances behind an Elastic Load Balancer (ELB). In order to ensure that the system is up-to-date and fault tolerant, active Amazon EC2 instances are periodically terminated and replaced with new instances. Because your application connects to an Amazon EC2 instance through the ELB, the connection becomes invalid when the Amazon EC2 instance is terminated. You should establish a new SMTP connection after you have delivered a fixed number of messages via a single SMTP connection, or if the SMTP connection has been active for some amount of time. You will need to experiment to find appropriate thresholds depending on where your application is hosted and how it submits email to Amazon SES.

  • You want to know the IP addresses of the Amazon SES SMTP mail servers so that you can allowlist the IP addresses with your network.

    The IP addresses for the Amazon SES SMTP endpoints reside behind load balancers. As a result, these IP addresses change frequently. It's not possible to provide a definitive list of all of the IP addresses for the Amazon SES endpoints. We recommend that you allowlist the amazonses.com domain, rather than allowlisting individual IP addresses.

SMTP response codes returned by Amazon SES

This section contains a list of response codes that the Amazon SES SMTP interface returns.

You should retry SMTP requests that receive 400 errors. We recommend that you implement a system that retries requests with progressively longer wait times (for example, wait 5 seconds before retrying, then wait 10 seconds, and then wait 30 seconds). If the third retry doesn't succeed, wait 20 minutes, and then repeat the process. To see an example of an implementation that uses an exponential retry policy, see How to handle a "Throttling - Maximum sending rate exceeded" error on the AWS Messaging and Targeting Blog.

Note

AWS SDKs implement retry logic automatically, but they use the HTTPS interface instead of SMTP.

If you receive a 500 error, you have to revise your request to correct an issue before you submit the request again. For example, if your AWS authentication credentials are invalid, you have to update your application to use the correct credentials before you submit your request again.

Description Response code More information

Authentication successful

235 Authentication successful

Your SMTP client successfully connected and signed in to the SMTP server.

Successful delivery

250 Ok MessageID

MessageID is a unique string of characters that Amazon SES uses to identify a message.

Service unavailable

421 Too many concurrent SMTP connections

Amazon SES can't process the request because there are currently too many connections to the SMTP server.

Local processing error

451 Temporary service failure

Amazon SES couldn't process the request. There might be issues with the request that prevent it from being processed.

Timeout

451 Timeout waiting for data from client

Too much time elapsed between requests, so the SMTP server closed the connection.

Daily sending quota exceeded

454 Throttling failure: Daily message quota exceeded

You've exceeded the maximum number of emails that Amazon SES permits you to send in a 24-hour period. For more information, see Managing your Amazon SES sending limits.

Maximum send rate exceeded

454 Throttling failure: Maximum sending rate exceeded

You've exceeded the maximum number of emails that Amazon SES permits you to send per second. For more information, see Managing your Amazon SES sending limits.

Amazon SES issue when validating SMTP credentials

454 Temporary authentication failure

Issues that could cause this issue include (but aren't limited to):

Problem receiving the request

454 Temporary service failure

Amazon SES didn't successfully receive the request. As a result, the message wasn't sent.

Incorrect credentials

530 Authentication required

The application that you use to send email didn't attempt to authenticate when it connected to the Amazon SES SMTP interface.

Authentication Credentials Invalid

535 Authentication Credentials Invalid

The application that you use to send email didn't provide the correct SMTP credentials to Amazon SES. Note that your SMTP credentials aren't the same as your AWS credentials. For more information, see Obtaining Amazon SES SMTP credentials.

Account not subscribed to Amazon SES

535 Account not subscribed to SES

The AWS account that owns the SMTP credentials is not signed up for Amazon SES.

Message is too long

552 Message is too long.

The message that you're trying to send is larger than the maximum message size.

Account not subscribed to Amazon SES

535 Account not subscribed to SES

The AWS account that owns the SMTP credentials is not signed up for Amazon SES.

MAIL FROM syntax error

553 <email-address> Invalid email address

There is a syntax error in the MAIL FROM part of the SMTP message. Please check that you are following the correct format and don't forget to enclose the email-address in '<>'.

RCPT TO syntax error

553 <email-address> address unknown

There is a syntax error in the RCPT TO part of the SMTP message. Please check that you are following the correct format and don't forget to enclose the email-address in '<>'.

User not authorized to call the Amazon SES SMTP endpoint

554 Access denied: User UserARN is not authorized to perform ses:SendRawEmail on resource IdentityARN

The AWS Identity and Access Management (IAM) policy or the Amazon SES sending authorization policy of the user who owns the SMTP credentials isn't allowed to call the Amazon SES SMTP endpoint.

Unverified email address

554 Message rejected: Email address is not verified. The following identities failed the check in region region: identity0, identity1, identity2

You're trying to send email from an email address or domain that isn't verified to send email from your Amazon SES account. This error could apply to the "From", "Source", "Sender", or "Return-Path" addresses. If your account is still in the sandbox, you also have to verify every recipient email address (except for the recipients provided by the Amazon SES mailbox simulator). If Amazon SES isn't able to show all of the identities that failed the verification check, the error message ends with three periods (...).

Note

Amazon SES has endpoints in several AWS Regions, and email address verification status is separate for each AWS Region. You have to complete the verification process for each sender in the AWS Regions that you want to use.
Note

For SMTP issues that aren't addressed by the troubleshooting on this page, try the SES support options listed under Contacting Us.