Deleting vs. archive
You can only delete contacts - there is no archive option. This means if deleted contacts are re-added they are treated as new contacts.
Deleting contacts cannot be undone
We keep backups for 30 days but recovery from the backups is a paid service. After 30 days contacts are removed from backups with no option to recover them.
Marking contacts as unsubscribed instead
Instead of deleting contacts you could mark them with consent = "revoked", essentially unsubscribing them. This way history is kept but contacts will not receive any emails from you going forward. You will not be able to re-import unsubscribed contacts as subscribed again.
Unsubscribed contacts aren't counted as active contacts for billing. Read more: how to bulk unsubscribe contacts.
Contacts with invalid emails
There is no need to delete contacts with invalid emails. Invalid and unsubscribed contacts don't count towards your total contact count and as such they aren't used for billing.
Unsubscribed and spam reported contacts
Contacts with consent status "revoked" or "spam reported" cannot be deleted. This restriction is in place to prevent these contacts from being (accidentally) re-added to the database as subscribed contacts, which could create spam complaints and compliance issues.
Re-importing contacts
If you re-import contacts who had been deleted they will be added as new contact records. Unsubscribed contacts cannot be deleted and during a re-import the unsubscribe status is retained. Unsubscribed contacts cannot be re-subscribed in bulk.
Loss of contact activity history
You permanently lose all history for deleted contacts such as email opens, sends, clicks, etc.
Email reports
Aggregate email stats are never removed even if the contacts the email was sent to no longer exist. You'll see for example that there were X clicks in an email but when you drill down you'll see fewer contacts if some of the contacts that are part of that metric are deleted.
User restrictions
Standard users (with no admin access) can only delete contacts that are shown on single page, for example 10, 25 or 50 at a time. Admin users can delete any number of contacts at once.
How to delete contacts?
After you reviewed the considerations above and decide that deleting is still your best option you can delete contacts using the "Group edit" option as described on the how to bulk edit contacts page.