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Call Us 1-800-383-5193

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SMTP errors in ec2 – How to resolve

by | Aug 16, 2021

Wondering how to resolve SMTP errors in ec2? We can help you.

Here, at Bobcares, we assist our customers with several AWS queries as part of our AWS Support Services.

Today, let us see how our Support Techs resolve it.

 

How to resolve SMTP errors in ec2?

Some of the common reasons for problems sending email from your instance over SMTP:

  • SMTP traffic is blocked by your security groups or network access control lists (network ACL) on default port 25, port 587, or port 465.
    Please note by default, outbound traffic is blocked on port 25 (SMTP) for all EC2 instances and AWS Lambda functions. To send outbound traffic on port 25, request the removal of this restriction.
  • The public IP address that was automatically assign to the instance change after a reboot.
  • Your outbound messages are flag as spam.
  • Emails aren’t delivered to a specific domain.
  • Outbound emails are delayed.
  • You can’t send emails even though you can receive them.

SMTP traffic is blocked by your security groups or NACLs on default port 25, port 587, or port 465

  1. To verify that traffic is block, check for connectivity at the SMTP port using Test-NetConnection or telnet utility.
  2. If traffic is block at the SMTP port, make sure that the following configurations are correct:The security group outbound (egress) rules must allow traffic to the SMTP server on TCP port 25, 587, or 465.

Firstly, the network ACL outbound (egress) rules must allow traffic to the SMTP server on TCP port 25, 587, or 465.
Secondly, the network ACL inbound (ingress) rules must allow traffic from the SMTP server on TCP ports 1024-65535.
The firewall and antivirus application on your Windows instance must allow traffic to the SMTP server on TCP port 25, 587, or 465.
The EC2 instance must have internet connectivity.

The public IP address that was automatically assign to the instance change after a reboot

Public IP addresses change after every reboot or instance stop and start.

To avoid this, make sure that the instance used as the mail server has an Elastic IP address assign to it.

 

Emails aren’t deliver to a specific domain

If you’re unable to send emails to a specific domain, do the following:

  • Firstly, verify if the recipient domain is blocking your IP address.
  • Then, make sure that your emails aren’t too large for the destination to accept.

Even if you don’t have a size restriction on sent mail, the recipient might have limits on incoming mail size.

The standard email size setting is 22 MB.

 

Outbound emails are delay

If your emails are delayed, do the following:

  1. Firstly, verify if the delayed emails are going to one specific address or domain.
  2. Then, check your email server configuration to make sure that nothing has changed.
  3. Verify if the email queue is slow on your server, or if emails leave your server on time, but are slow to arrive at the destination.
    If emails are stacking in the queue on your server, make sure that there aren’t performance issues on your SMTP server.
    If the problem is at the destination, make sure that your emails aren’t too large for the destination to accept. Even if you don’t have a size restriction on sent mail, the recipient might have limits on incoming mail size. The standard email size setting is 22 MB.
  4. Finally, analyze the message header using an email header analyzer tool to look for diagnostic information.

 

[Need help to resolve similar errors? We’d be happy to assist]

 

Conclusion

In short, we saw how our Support Techs resolve SMTP errors in ec2.

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