Important steps for working with an email database include:
Removing duplicate emails (+ merging addresses of the same contact).
Removing non-existent addresses.
Excluding addresses for spam detection.
Correction of typos.
Filling in contact information (full name, date of birth, gender and other personal information used for personalization and segmentation).
Separating unsubscribers and complainers into separate lists.
Resuscitation of sleeping (inactive) contacts.
Let us consider individual points in more detail.
Cleaning the contact database from duplicates
Where do duplicates come from?
Most often, due to repeated user registrations (filling out one or different subscription forms). But there may be other sources: for example, errors during import, export, manual entry of contacts, etc.
Why do you need to clean your database of duplicate emails?
To save the number of sendings and not to send the same taiwan phone number data letters to one recipient. And also, due to duplicates, individual mailing indicators may suffer (opening rate, complaints, conversion rate, etc.).
When should this be done?
Immediately when launching the first mailing to a new database, when loading the contact database into a new mail service (when moving), and also at certain intervals (once a month/six months, whichever is more convenient for you, and depending on how quickly the contact database fills up/how big it is).
How to clean
You can use various improvised means, for example:
Microsoft Excel tables (Data tab, Working with data section, Remove duplicates item);
Google Spreadsheets (Data –> Clean Data –> Remove Duplicates);
external services for validation and cleaning of lists (if you are not afraid to trust your data to strangers);
email distribution services (if such a possibility is available, for example, RuSender automatically removes duplicates and can update missing contact information during import).