SmartPop limitations

SmartPop mail delivery problems

We are often asked “Why do I get the message ‘SmartPop Mail Delivery Failure?”. This article will explain why it happens and what can be done about it.

History of SmartPop.

Many ISP’s offer multiple mail addresses with their mail accounts, but place all the messages in a single mailbox. So for example you might have the email addresses, and, and all the mail might be placed in a mailbox This type of mailbox is commonly known as a domain or multi-drop mailbox.

The problem with a multi-drop mailbox is that the first person to connect to it gets all the mail regardless of who it was sent to. SmartPop solves this problem by retrieving the mail messages and then delivering to the appropriate local mailbox.

To deliver the mail from the example above, the administrator would install FTGate, create three mailboxes (user1, user2 and user3) in the domain “”, then create a SmartPop account for SmartPop would then collect the mail and deliver it to the appropriate user.

What is a message

An Internet mail message consists of two parts, the header and the body. The header contains information such as who the message is from, who it is to, the subject, when it was sent etc. The body is the text of the message.

How is mail transferred around the Internet.

Most mail is transferred from point to point using a protocol called SMTP (Simple Mail Transfer Protocol). This protocol transfers a message by making a connection to a destination computer, sending the Envelope of the message and then sending the message. The Envelope of the message contains the senders email address and one or more recipients addresses.

By the time the message reaches your ISP’s machine the envelope will usually consist of the sender and one recipient. It is this recipient address that the ISP uses to determine which mailbox should be used for storing the message. In the above example a message to user1, user2 or user3 would be written to a single mailbox (

After the mail is placed in a mailbox it can be retrieved using a protocol called POP3 (Post Office Protocol version 3). This protocol transfers the body of the message. The problem with this protocol is that it was only designed to access mailboxes that had mail for a single user.

What can go wrong to cause delivery failures ?

A message is in the ISP mailbox for an address that doesn’t have a local mailbox.


If using the above example a message was in the ISP mailbox addressed to, SmartPop would not be able to deliver it as there is no mailbox or alias for that name. This can be fixed by creating the mailbox or alias.

The message was sent to the ISP mailbox by a mailing list that doesn’t include the recipients address (BCC).


Many mailing lists do what is known as blind mailing. This is where the message header has a TO: line to say Obviously there is no mailbox on the local mail system called that, so this causes an error. The second problem is harder to fix and will require your ISP’s help. I will describe the problem using an analogy with the postal mail system.

A letter is sent inside an envelope (SMTP is the envelope) addressed to Fred Bloggs. The letter inside starts Dear Sir (the message header). The postman (your ISP server) brings the letter to your office but before delivering it takes the letter out of the envelope and puts only the letter through the postbox at the front door (ISP pop3 mailbox). Now when your secretary (FTGate) collects the mail, there is no indication as to who the “Dear Sir” is, so it cannot be delivered.

The Solution

Many ISP’s copy the envelope (SMTP) address into the message header, that way the messages recipient address can always be found. There is no standard for the way that they do this and FTGate has been coded with most of the methods in use. This allows SmartPop to read the message header and deliver to the correct mailbox.

If your messages are being delivered as “SmartPop mail delivery failure”, you should check the header of the attached message to see if the correct address exists. If it does not, you need to contact your ISP and arrange for them to either add the additional field for the envelope to the message headers or give you an SMTP feed. If they are not prepared to do this then consider changing to another ISP as a multi-drop mailbox will not work correctly without the addition of the extra header information.

Example Headers

An example of a message (sent to that has not had the ISP include the additional envelope data might be:


Date: Fri, 26 Jun 1998 08:40:45 -0400


From: Fred Bloggs <>

Subject: Version and “Received… for”




and an example that has had the additional information included might be:



Date: Fri, 26 Jun 1998 08:40:45 -0400


From: Fred Bloggs <>

Subject: Version and “Received… for”




Note the additional highlighted line. Without this line the ISP has made it impossible to deliver the message correctly. They have discarded the delivery information. If your ISP does not include this information you should contact them and ask that they add the information or explain to you how you are supposed to know who the message is for.

We hope that this goes some way towards explaining the problem.