Emails via Forward Email, a free email forwarding service for custom domains were having trouble reaching Gmail due to errors like Delivery Status Notification (Failure) and Delivery Status Notification (Delay).

Background: Got registered on Forward Email's denylist

Emails via Forward Email were experiencing Delivery Status Notification errors and not reaching Gmail properly, so I investigated the issue for this article.

The reason was that I was sending emails from contact forms to custom domain email addresses via Forward Email, which resulted in sending spam emails to Gmail through Forward Email. As a result, I got registered on Forward Email’s denylist.

Email subject: `Delivery Status Notification (Delay)`

Here’s an example of the email body:

Delivery incomplete There was a temporary problem while delivering your message to [email protected]. Gmail will retry for 46 hours and notify you if the delivery fails.

Response from remote server: 421 The address [email protected] is denylisted by https://forwardemail.net. To request removal, you must visit https://forwardemail.net/[email protected].; If you need help, forward this email to [email protected] or visit https://forwardemail.net. Please note we are an email service provider and most likely not your intended recipient.

Final-Recipient: rfc822; [email protected] Action: delayed Status: 4.0.0 Remote-MTA: dns; mx1.forwardemail.net. (138.197.213.185, the server for the domain example.com.) Diagnostic-Code: smtp; 421 The address [email protected] is denylisted by https://forwardemail.net. To request removal, you must visit https://forwardemail.net/[email protected].; If you need help, forward this email to [email protected] or visit https://forwardemail.net. Please note we are an email service provider and most likely not your intended recipient. Last-Attempt-Date: Mon, 20 Mar 2023 22:23:59 -0700 (PDT) Will-Retry-Until: Wed, 22 Mar 2023 20:53:43 -0700 (PDT)

---------- Forwarded message ---------- (Adult site redirect text and links were included)

Email subject: `Delivery Status Notification (Failure)`

Here’s an example of the email body:

Mail delivery error There was a problem delivering your message to [email protected]. Please check the detailed technical information below or try resending in a few minutes.

Response from remote server: 421 The address [email protected] is denylisted by https://forwardemail.net. To request removal, you must visit https://forwardemail.net/[email protected].; If you need help, forward this email to [email protected] or visit https://forwardemail.net. Please note we are an email service provider and most likely not your intended recipient.

Final-Recipient: rfc822; [email protected] Action: failed Status: 4.0.0 Remote-MTA: dns; mx2.forwardemail.net. (104.248.224.170, the server for the domain example.com.) Diagnostic-Code: smtp; 421 The address [email protected] is denylisted by https://forwardemail.net. To request removal, you must visit https://forwardemail.net/[email protected].; If you need help, forward this email to [email protected] or visit https://forwardemail.net. Please note we are an email service provider and most likely not your intended recipient. Last-Attempt-Date: Tue, 21 Mar 2023 20:59:45 -0700 (PDT)

---------- Forwarded message ---------- (Suspicious Russian text and redirect links were included)

That’s all from the investigation of Forward Email emails experiencing Delivery Status Notification errors and having trouble reaching Gmail. That’s all from the Gemba.