Resolving SMTP Failures on AWS-based Server

This article applies to all versions of SmarterMail.
When SmarterMail is installed within Amazon Web Services (AWS) infrastructure, SMTP failures and/or timeouts may prevent or delay email delivery.

This issue is due to the default configuration of a new Windows server that's deployed to the AWS infrastructure. SMTP communication is blocked by default, preventing SmarterMail from functioning properly. Furthermore, AWS disables Jumbo Frame support in Windows by default, meaning SMTP sessions may fail even after SMTP communication has been unblocked. To resolve the SMTP failure/delay, you must (a) request SMTP access to be unblocked, and (b) modify the Jumbo Frame configuration to allow SMTP sessions to complete. 

a. Follow these steps to request SMTP access for the AWS-based SmarterMail server: 

  1. Ensure an elastic or static IP address is associated with your SmarterMail instance. 
  2. Configure DNS records for the public IP address. (A record and PTR records are required at minimum.)
  3. Complete the SMTP unblocking form from the AWS website. The form can be found here: https://aws-portal.amazon.com/gp/aws/html-forms-controller/contactus/ec2-email-limit-rdns-request. Please note that it may take a few hours for the request to be approved.

b. Follow these steps to modify Jumbo Frame support in Windows to allow SMTP sessions to complete:

  1. Log in to the Windows server where SmarterMail is installed, and open the Network & Sharing Center.
  2. Click the Change Adapter Settings link on the left side of the screen.
  3. Right-click on the public network interface and select Properties.
  4. Under the Networking tab, click the Configure button for the network adapter.
  5. Click on the Advanced tab, locate Jumbo Packet and increase the value, as needed.
  6. Click OK to close the dialog windows. Note that when you make this change, the NIC will lose network connectivity for a few seconds. You should also reboot to ensure the change has taken effect.

Once you've completed these steps, your AWS-based SmarterMail instance should complete SMTP sessions as expected. 

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