How to check the quality of a database

How to check the quality of a database

It's always best to create your own subscriber database. Preferably use the double opt-in method, as this is more efficient for generating high quality databases.


But sometimes this isn't possible, you're not interested or you simply need to send a mass mailing campaign as soon as possible. Whatever the reason, you preferred to purchase a legitimately created database from an online provider.


 How do you know if a purchased database is of high quality?

This is not a trivial question, as the success of your email campaign depends on it, as well as your sender score reputation.

Many customers have asked us for information on how to analyze the quality of a database and how to detect possible problems. The main aspects you should check before sending an email marketing campaign are:

1. check for duplicate emails and syntax errors in email addresses.

2. Check the number of bounces

3. check for suspicious or problematic emails

4. Check for emails that have complained about spam or unsubscribed.

5. Check if it is an active database

6. Check if the emails are public and request proof of signup.

7. Prepare a preliminary pilot to review the results.

We'll explain these points in detail below and in order.

First of all, let's start from the fact that we are working with a legitimate database acquired from a co-registration provider, sector portals, agreements with companies, etc.

The subscribers added to this database have given their registered, verified and consented permission for the sending of promotional emails, mass mailing campaigns and other marketing campaigns.

They are aware of the transfer of their data for this purpose.

Let's start from this assumption, so when acquiring a subscriber database, above all: make sure that the data has been collected in accordance with the law and that the subscribers have given their consent.

Otherwise, your email marketing campaign will be a failure before it even begins. It is always advisable to take the time to ensure the quality of the list and check legal aspects before you start.

Assessing the quality of the database you have acquired

There are several potential problems with a database that can ruin your email marketing strategy. These include spamtraps, old lists and bounces, spam complaints, etc.

Let's see how to detect these problems using Mailrelay's features.

Checking emails for duplicates and syntax errors

The most basic aspect of creating an up-to-date and properly maintained subscriber database is detecting duplicate or incorrect emails with syntax errors.

For example:,, or similar addresses.

If we do a quick check and there are errors, we should ask for explanations, because if they haven't taken care of something so basic, we can hardly expect that in other more advanced considerations they have taken more care.

When you import a database to your Mailrelay dashboard, many of these errors are detected automatically:

If you see a lot of errors after the import, be wary of the quality of the database.

Check the number of bounces

A quality database must be up-to-date, so there should be no bounced emails or emails with errors.


To check this, you can upload the contacts to Mailrelay and check how many bounces have been confirmed in the subscribers section (more information in "How Mailrelay manages bounces"):

If the database is really high quality and up-to-date, this percentage should never exceed a maximum of 5%.

Otherwise, it is probably old and can therefore cause problems, even with valid emails, because they may not remember where they registered and may report the campaign as spam.

Excessively high bounce rates are detrimental to your sender reputation.

There is no point in acquiring a database to launch an email marketing campaign, if no one receives the email because the addresses are wrong, incorrect or too old.

Check for suspicious or problematic emails.

This must be done manually.

We have to look out for suspicious emails, such as,, etc., which can be a clear indicator that registered users have entered false data or accounts that they have no real intention of using.

This is often the case if the information has been collected at fairs, events, sweepstakes and so on, when users have entered their data manually.

Whether it was done intentionally or by mistake, we can find these emails. 

And if we find some of them, we should ask the provider for an explanation, as they should have cleaned the database beforehand.

Check for emails that have been reported as spam or requested to be removed.

To do this, we should cross-reference the list of unsubscribes and spam complaints in our account and check for matches:

You can also contact Mailrelay's Customer Service Department for a more comprehensive study with empirical data from our platform.

But first of all, if the database has spam complaints, we should question its quality.

Check that it is an active database

We should ask the provider for a list of the database's activity over the last 3 months.

In other words, if the list is really double opt-in and engaged, the results in terms of click-through rates and openers should be proportionately relevant. 

This aspect is related to the point about bounces.

An active database should have a lower volume of bounces because, as subscribers are updated, bounced emails should be "cleaned".

Sending a mass mailing campaign to a database that has been inactive for a long time can seriously affect your sender score reputation.

Check if they are public emails and request the log.


This is another aspect that can be checked manually. We can randomly select some emails and search Google with quotes to see if they are available on web pages.

If all or most of them are found, it is very likely that this is a database created from public listings and not active records.


It doesn't hurt to choose several random emails and ask the provider for the log of records and confirmation of them with source IPs, time and date of registration.

Create a pilot test for a preliminary check

Finally, before sending to the entire database, it is advisable to run a test with a random 10% of the database.

This way, you'll be able to see the results; you could also randomly contact subscribers so that they can confirm their registrations and veracity.

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