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Non-deliverable International Mail: An accidental real-world test


This paper was distributed at the Plenary meeting of the Consultative Committee of the UPU in Bern last week.  It is an important view of a problem seen in an entirely new light that should give thoughtful pause to any international mailer who thinks he knows what his response rate is. It is also in the Address Library. Editor.

Non-deliverable International Mail Returns:  An accidental real-world test


How do you know if your mail arrived?

Earlier this year, WorldVu did an international mailing that has turned into an accidental test on the treatment of non-deliverable international addresses.  Using a rental list supplemented by some in-house addresses, we did a small test mailing to determine the effectiveness of three different marketing pieces to a number of countries where we have good markets.

We mailed a standard business envelope, a “flat”(a multi-page brochure like a magazine), and a CD to each of the addresses. We used first-class mail, which is the highest rate.  The test design let us know when the pieces arrived because we conducted a follow-up interview via email or telephone call to the participants.  It worked well, with no major problems.  The feedback gave us the information we were looking to gather.    However, it highlighted some difficulties posed for mailers by international non-deliverable addresses.

More pieces failed to reach the participants than we anticipated.  Over the months following the study, some of the pieces that did not reach the participants have arrived back in our office and were neatly piling up in a corner of the office – each marked with the date it was received here.  Non-deliverables are costly and annoying.  When the list is international addresses, it’s even more costly with higher rental and higher postage costs. And, sadly, many other pieces were never seen again by either ourselves or the addressees.

While this was not a scientific sample – it was an accidental test within our marketing test! – the results do have some troubling aspects.  I have eliminated a few of the returns from the analysis where there was an issue that did not involve the address.  For example, one recipient’s assistant refused to accept an item, a CD, because of the outrageous taxes demanded by Customs.  It was returned.  It is acknowledged that not all countries were covered by the mailing and, of course, the intent was to use deliverable addresses.

The undeliverable returns took an average of 56.21 days from the date of mailing to arrive back at our office with a median of 42 days.  (Half of the returns took more than 42 days and half took less than 42 days.)  The first return arrived from Ireland 9 days after the mailing and the final one from the United Kingdom came back 129 days after it was mailed.  In general, more of the business envelopes were returned more quickly.  The CD’s disappeared at the highest rate.  The chart below gives some details on the average time for returns by country.


Average days from mail date to return





Hong Kong








New Zealand


United Kingdom


In addition to the non-deliverable returns, some pieces never made it to their destinations and were not returned.  The countries in which items were not received and none returned were: Argentina, Australia, Belgium, Bermuda, Brazil, Nigeria, Pakistan, South Africa, Switzerland, and Taiwan.

This is frequently a hidden problem for mailers.  Marketers, who are by nature trusting of infrastructures, generally assume that lack of response is really simply a low response rate, and that some cities or countries tend to have low response rates.  But one is never sure.  It could be simply that the infrastructure does not function to either deliver, or return undeliverable mail.  Because of the nature of our study, we could track this.   In the case of our test, was it due to a flaw in our test design?  Since over 98% of the pieces mailed can be accounted for, I do not think it is a design issue. 2% of our mailed pieces went undelivered and unreturned.

Each country has its own rules on how to handle non-deliverables. Often, domestic and international items are treated differently in different  countries.  The policies range from returning the pieces to the sender at no additional fee to discarding them.  In some cases, one can arrange for non-deliverable returns for a fee, sometimes only if the returns go to a domestic address (or a foreign address from the mailer’s point of view).  The information on the returned piece also varies by country and may include the reason the item is undeliverable, a forwarding address, or simply “Undeliverable”.

Obviously, not knowing whether something arrives or not is very disturbing.  How can one tell a good address from an undeliverable one?  All these addresses were formatted correctly.  For those using postal codes, all the codes were the correct length and in the correct range.  Equally troubling to me is that some items to the same addresses were delivered and some were returned as non-deliverable.  I am not sure what this will mean to our future policies on file-cleaning.  In our marketing campaigns, do we mail those addresses again to see what happens? Taken altogether, this shows the importance of address hygiene and a major problem in the international postal system.  No mailer can depend on returns to clean an international list.  Moreover, that 2% of the mailing was neither received nor returned may underline the for on-going address hygiene and verification, or it may underline the reliability of the postal system in question.

In addition to the importance of list hygiene, this accidental test also highlights the need for consistent world-wide systems of (1) address correction and (2) return of non-deliverable items by all of the postal administrations.  Some postal administrations cite privacy regulations and others point to costs as reasons to not provide non-deliverable returns to the mailer or not provide further information.  Standards for this would greatly assist mailers and encourage more accurate addressing.

Contributed by Ms. Merry Law, President, WorldVu, Inc.  (To contact Merry, email the Editor@

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