Quick answer
Data cleansing for a mailing means checking and correcting a list before anything is printed, so you only pay to print and post pieces that can reach a real, willing recipient. The core steps are PAF validation (checking every address against Royal Mail's Postcode Address File of around 32 million UK delivery addresses), de-duplication (removing repeated people and households), suppression against the Mailing Preference Service and gone-away files, and formatting names and addresses so they print cleanly. Under UK GDPR, personal data must be accurate and, where necessary, kept up to date, so cleansing is a compliance step as well as a cost saving.
Key takeaways
- PAF validation checks each address against Royal Mail's Postcode Address File, which lists around 32 million UK delivery addresses and changes every week.
- De-duplication should work at person and household level, and against previous send lists, not just exact matches.
- Screening non-customer lists against the Mailing Preference Service is a condition of DMA membership, and the DMA says members are responsible for their suppliers' screening too.
- Every undeliverable item wastes print and postage. On Royal Mail's April 2026 rate card, a 2nd Class Mailmark Unsorted Advertising Mail letter cost 42.9p–44.8p in postage alone.
- UK GDPR's accuracy principle says personal data must be accurate and, where necessary, kept up to date. Delivery addresses are one of the ICO's own examples.
What data cleansing means for a mailing
Every mailing list decays. People move, die, change their names, ask not to be contacted or end up on your file twice. A list that was accurate last year will have errors in it today, and each error is a pack you pay to print, enclose and post that will never reach the person it was meant for.
Data cleansing (also called list hygiene) is the work done before production to find and fix those errors. For a mailing house it is the first stage of every job, not an optional extra. At Fretwell, our data processing team runs every list through validation, de-duplication and suppression before a single sheet is printed.
- 1
Receive the data securely
Files arrive by secure SFTP, encrypted in transit and at rest. Never email a mailing list as an attachment.
- 2
Format and standardise
Split names into title, first name and surname, put address lines in a consistent order and correct obvious keying errors, so every record prints the same way.
- 3
Validate against PAF
Match each address to Royal Mail's Postcode Address File, correcting postcodes and filling in missing address elements.
- 4
De-duplicate
Find repeated records within the file, across files and against previous send lists.
- 5
Suppress
Remove people who have registered with the Mailing Preference Service, people known to have gone away, and anyone on your own do-not-mail list.
- 6
Report back
You receive counts for each stage, so you can see what was removed and why, and update your own database.
PAF validation: getting the address right
The Postcode Address File (PAF) is Royal Mail's database of every UK delivery address. It holds around 32 million delivery addresses and 1.8 million postcodes, and it is updated constantly as new homes are built and addresses change. Royal Mail's PAF site reports thousands of changes in a typical week.
PAF validation matches each address on your list to a PAF record. Where the match is close but not exact, the address is corrected: a wrong postcode is fixed, a missing house number or street name is filled in, and the address lines are put in Royal Mail's standard order. Addresses that cannot be matched at all are flagged so you can decide whether to mail them.
Clean addresses matter for postage as well as delivery. Royal Mail's discounted services, including Mailmark, sort mail by machine using the postcode and barcode, and Mailmark reporting flags items with poor address data. Accurate postcodes are what allow a mailing to be sorted for the best available rate.
PAF does not tell you who lives there
PAF confirms that an address exists and is formatted correctly. It does not confirm that the person on your list still lives there. That is what gone-away and other suppression screens are for.
De-duplication: one pack per person (or household)
Duplicates creep in when lists are merged, when the same person signs up twice, or when one record has "Mrs J Smith" and another has "Jane Smith" at the same address. Sending two identical packs wastes money and tells the recipient you do not know who they are.
| Level | What it removes | When to use it |
|---|---|---|
| Exact match | Records that are identical in every field | Always, as a minimum |
| Person level | The same person recorded in different ways (initial vs first name, typos, old and new formats) | Most mailings, especially merged lists |
| Household level | Different people at the same address, leaving one pack per household | Acquisition mailings and catalogues where one pack per home is enough |
| Against previous sends | People already mailed in an earlier wave or in another of your campaigns | Multi-wave campaigns and when combining rented and in-house lists |
| Against your own suppressions | Existing customers, complainants, staff or anyone you have agreed not to mail | Always |
Matching is a judgement call, not just a setting. Too loose and you remove genuinely different people; too tight and duplicates slip through. Agree the rules before the job runs, and check a sample of the records that were removed.
Cleansed, personalised and posted under one roof
We validate, de-duplicate and suppress your data, then print, enclose and sort the mailing in-house in Keighley.
Explore the serviceSuppression screens: MPS, gone-aways and deceased
Suppression means removing records that are valid addresses but should not be mailed. The main screens used in the UK are below.
| Screen | What it catches | Where the data comes from | How often to screen |
|---|---|---|---|
| Mailing Preference Service (MPS) | People who have registered not to receive unsolicited advertising mail | The MPS register, run by the Data & Marketing Association. There are two files: MPS Original (household level) and MPS Personal (individual level) | Before every advertising mail campaign. The register is updated daily |
| Gone-away files | People who have left the address you hold for them | Commercial gone-away files compiled by data providers | Before each mailing, especially for older lists |
| Change of address (NCOA) | Movers, with their new address where they have registered for redirection | Royal Mail's National Change of Address data, licensed through data providers | Before each mailing to existing customers or supporters |
| Deceased files | People who have died | Registers such as The Bereavement Register and other commercial deceased files | Before each mailing |
| Your own do-not-mail list | Anyone who has asked you directly to stop, plus complainants | Your own records | Always |
We run MPS suppression and gone-away suppression as part of our standard hygiene workflow. Change-of-address and deceased screening use data licensed from third-party providers. Ask us what we can arrange for your file, or supply a file that has already been screened.
Is MPS screening a legal requirement?
MPS describes screening as part of the industry's self-regulation rather than a legal duty. But it is a condition of DMA membership, and the DMA says members are responsible for their suppliers' actions, so if a mailing house handles your list, it is still your job to make sure it is screened. Screening is also an easy way to show you respect people's wishes, which matters when you rely on legitimate interests for marketing mail.
Deceased screening deserves particular care. Mailing someone who has died causes real distress to their family, and charity and financial services mailings are the most likely to reach recently bereaved households. See our charity sector page for how we handle donor data.
Why cleansing pays for itself
The saving is simple arithmetic: every record you remove before production is a pack you do not print, enclose or post. Postage is usually the biggest part of that cost. On Royal Mail's April 2026 rate card, an Advertising Mail letter up to 100g cost 42.9p–44.8p on 2nd Class Mailmark Unsorted and 29.0p–30.4p on Economy Low Sort Mailmark, before print and enclosing are added.
32m
UK delivery addresses on Royal Mail's Postcode Address File
Source: Royal Mail PAF, 2026
42.9p–44.8p
Postage per 2nd Class Mailmark Unsorted Advertising Mail letter (up to 100g)
Source: Royal Mail, April 2026
Daily
How often the MPS register is updated
Source: MPS licensee FAQs
There are less obvious savings too. Clean, PAF-validated data sorts better, which helps you qualify for the cheaper sorted postage options. Fewer packs go to the wrong person, so fewer complaints come back. And the counts from each cleanse tell you how healthy your database is, which helps you plan. For a full breakdown of campaign costs, see how much direct mail costs in the UK.
Cleansing also supports compliance. The ICO's guidance on the accuracy principle says you may need to keep personal data up to date depending on what you use it for, and gives delivery addresses as an example. Running a list through validation and suppression before each mailing is a practical way to take reasonable steps. Once the data is clean, it can drive personalised content as well as the address.
Sources
- Royal Mail – Powered by PAF (Postcode Address File)
- MPS – Licensee FAQs (Data & Marketing Association)
- Mailing Preference Service – consumer site
- ICO – Principle (d): Accuracy
- Experian – Identity data cleansing (deceased, goneaway, NCOA and MPS)
- Experian – What is the Bereavement Register?
- Royal Mail – Retail Letters Price Guide, prices effective 7 April 2026 (archived copy)
