Sending email with AWS SES via SMTP,error 421 - amazon-web-services

Question

So I have a domain purchased through SES which I have verified with SES.I have tested that sending/receiving works by signing into the email with the workmail web app.I am getting the following error when trying to send email with my spring app.
javax.mail.MessagingException: Could not connect to SMTP host: email-smtp.eu-west-1.amazonaws.com, port: 25, response: 421
Appconfig.Java
#Configuration
#PropertySource("app.properties")
#EnableTransactionManagement
public class AppConfig {
#Autowired
private Environment env;
#Bean
public JavaMailSender getJavaMailSender() {
JavaMailSenderImpl mailSender = new JavaMailSenderImpl();
mailSender.setHost("email-smtp.eu-west-1.amazonaws.com");
mailSender.setPort(25);
mailSender.setUsername("noreply#mydomain.com");
mailSender.setPassword("mypassword");
Properties props = mailSender.getJavaMailProperties();
props.put("mail.transport.protocol", "smtp");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.starttls.required", "true");
props.put("mail.debug", "true");
return mailSender;
}}
EmailServiceImpl.java
#Component
public class EmailServiceImpl {
#Autowired
public JavaMailSender emailSender;
public void sendSimpleMessage(String toAddress, String subject, String text)
{
SimpleMailMessage message = new SimpleMailMessage();
message.setTo(toAddress);
message.setSubject(subject);
message.setText(text);
emailSender.send(message);
}
}
EmailServiceImpl is autowired into my web controller where I send an email after generating a password reset token

Answer 1

First of all,you have done everything right as said in the AWS docs.
You are right in using your smtp credentials as you are using their smtp interface to send mail,and not their aws sdk(if you use,aws sdk,you have to use acces key and password).
But,here comes some other issues which might help you resolve the issues which we have to do as it is not there in the docs.
You have to troubleshoot the error code sent by smtp.
Mostly,SMTP error code 421 shows up when the recipient mail server is very busy as it is receiving a lot of messages,so it temporarily defers your message by giving this error code or your recipient client have some problems.
You can study here.
https://sendgrid.com/blog/smtp-server-response-codes-explained/#:~:text=421%20%E2%80%93%20Your%20message%20was%20temporarily,locked%20or%20is%20not%20routable.
https://www.arclab.com/en/kb/email/smtp-response-codes-error-messages.html#:~:text=The%20SMTP%20error%20421%20is,see%20SMTP%20Error%20451%20below).
You can try sending the mail after sometime or you can try sending with different port.
My Incident:
I was using AWS SES for sending mail from my Springboot Application.
I was also using SMTP interface of AWS ses like you.
There are 3 ports which are listed on AWS management console to send mail.
But,when I was using Port 465,it was not working.
But,when I was using Port 25 or Port 587,it was working.
But,even then,It is always recommended to use 587 as it is recommended by IETF and is safest to use with TLS.
Using Port 465 is least recommended.You can study here but AWS supports it.There are many clients still supporting it but it is not widely in use.
As,I told you in my case it was failing.
You can study here about all the 3 ports and how port 465 functioning is different from port 25 and 587
But,you can solve the issue of port 465 by using smtps protocol with it.
Port-25,587(use smtp as protocol)
Port-465(use smtps as protocol,as in this case client has to initiate the tls encryption)
https://docs.aws.amazon.com/ses/latest/DeveloperGuide/smtp-connect.html
You can get a guide from where to chose a port.
https://pepipost.com/blog/25-465-587-2525-choose-the-right-smtp-port/

Answer 2

You are using port 25. SES uses port 465 or 2465. Also remember to use SES SMTP credentials and not your IAM credentials (AccessKey).
Connecting to the Amazon SES SMTP Endpoint