EmailDiscussions.com - View Single Post - Bounce Back Email: Fault of Sending ISP or Receiving Hosting Co?

n5bb · 28 Jan 2017, 12:45 PM

Welcome to the EMD Forums!

The term "bounce back" is not very precise. What the sender received from Comcast is clearly identified as a "Delivery Status Notification" (often referred to as DSN) message. The headers you posted are not important, since that message was generated by Comcast to inform the sender that there was a permanent error delivering the message. As you can see below, the root cause might be DNS configuration by the owner of the destination domain (probably you), a secondary DNS cache somewhere, or Comcast.

The important information which is missing in your post is everything after "Reason: Permanent Error." in the body of the DSN message. The exact wording and any error numbers are important. For instance, see:
http://postmaster.comcast.net/mail-error-codes.html

So what appeared to happen is:

The message arrived at the Comcast outgoing server. We can't tell from what you posted if it was a forwarding rule or a Comcast customer sending from their Comcast email account.
The Comcast server found a reason not to send the message to the destination. The failure was permanent, which means it's not due to a temporary communication problem.
The Comcast server sent a DSN to the sender warning them about the problem. More about the cause is probably included in the body of the DSN message.

Possible causes include:

An outgoing spam filter at Comcast is preventing some types of messages from being sent by their servers, a problem discovering a route to the destination address (such as if the MX records for your domain could not be found or were corrupted), or some other permanent addressing failure (such as your MX records pointing to a target IP which is blocked by Comcast or for some other reason is permanently unreachable).
Another example of a possible problem might be DNS caching and TTL (Time To Live) for your MX DNS record. Let's say you have a long TTL set for your DNS. When you change the MX pointer the previous TTL setting governs how long the old target will linger in DNS caches. If for some reason Comcast has a slow DNS cache update (or you don't wait long enough after changing the MX record), the messages might be targeting an old IP which can't be reached.
It's also possible that the MX record is corrupted for some other reason at Comcast. Do you have at least two MX entries to different target IP receiving servers? Have you carefully manually checked (or used online DNS checking services) that there is nothing corrupted in your DNS records (especially MX)?
Another possibility is that you are pointing your MX record to a CNAME alias in your DNS records. That's a bad idea, and might result in some servers not being able to resolve the destination IP for your incoming server. See:
https://exchangepedia.com/2006/12/sh...s-aliases.html

Bill

28 Jan 2017, 12:45 PM	#2
n5bb Intergalactic Postmaster Join Date: May 2004 Location: Irving, Texas Posts: 8,929	Delivery Status Notification & some possible causes Welcome to the EMD Forums! The term "bounce back" is not very precise. What the sender received from Comcast is clearly identified as a "Delivery Status Notification" (often referred to as DSN) message. The headers you posted are not important, since that message was generated by Comcast to inform the sender that there was a permanent error delivering the message. As you can see below, the root cause might be DNS configuration by the owner of the destination domain (probably you), a secondary DNS cache somewhere, or Comcast. The important information which is missing in your post is everything after "Reason: Permanent Error." in the body of the DSN message. The exact wording and any error numbers are important. For instance, see: http://postmaster.comcast.net/mail-error-codes.html So what appeared to happen is: The message arrived at the Comcast outgoing server. We can't tell from what you posted if it was a forwarding rule or a Comcast customer sending from their Comcast email account. The Comcast server found a reason not to send the message to the destination. The failure was permanent, which means it's not due to a temporary communication problem. The Comcast server sent a DSN to the sender warning them about the problem. More about the cause is probably included in the body of the DSN message. Possible causes include: An outgoing spam filter at Comcast is preventing some types of messages from being sent by their servers, a problem discovering a route to the destination address (such as if the MX records for your domain could not be found or were corrupted), or some other permanent addressing failure (such as your MX records pointing to a target IP which is blocked by Comcast or for some other reason is permanently unreachable). Another example of a possible problem might be DNS caching and TTL (Time To Live) for your MX DNS record. Let's say you have a long TTL set for your DNS. When you change the MX pointer the *previous* TTL setting governs how long the old target will linger in DNS caches. If for some reason Comcast has a slow DNS cache update (or you don't wait long enough after changing the MX record), the messages might be targeting an old IP which can't be reached. It's also possible that the MX record is corrupted for some other reason at Comcast. Do you have at least two MX entries to different target IP receiving servers? Have you carefully manually checked (or used online DNS checking services) that there is nothing corrupted in your DNS records (especially MX)? Another possibility is that you are pointing your MX record to a CNAME alias in your DNS records. That's a bad idea, and might result in some servers not being able to resolve the destination IP for your incoming server. See: https://exchangepedia.com/2006/12/sh...s-aliases.html Bill