Every bulk upload is logged. Import history is the answer to "where did these contacts come from" and "did that file actually work".

#What each entry shows

Field	Means
File name	What you uploaded
Total records	Rows in the file
Imported	Contacts successfully created
Failed	Rows that did not make it, with the reason
Auto-generated values	Contacts imported with a generated name, or flagged Cannot be contacted because the row had no real email or phone at all
Merged	Rows that matched an existing account closely enough to be merged into it rather than imported as new
Completed	When it finished

#Getting there

From Accounts → Import History, or by clicking View Details on the notification you get when an import finishes. View Details also shows the tag applied to that run and its own Merged records list.

#What to check after an import

1
Does imported plus failed equal your total?
If not, and your file was over 2,000 rows, the rest was left behind. See Bulk upload.
2
How many are flagged Cannot be contacted?
Those rows had no email or phone at all, nothing was invented to fill the gap. Fix them from Accounts list → Email Updates.
3
Read the failures.
They are usually one systematic problem rather than many individual ones.

#Cleaning up a bad import

Deleting a history record only removes that log entry, the contacts it created or merged into stay exactly as they are in Accounts. Import History alone cannot tell you which Accounts-list rows came from a run once its record is gone, so identify the contacts first, then clean up in this order.

1
Open View Details for the run and note the tag applied to it, and its Merged records list.
2
Go to the Accounts list and search by that tag.
3
Use Bulk Delete Accounts on the results.
Only accounts with zero linked records (opportunities, listings, bids, notes) are eligible, the rest are skipped with a reason shown.
4
Come back here and delete the record for that run.
Single record, several selected, or delete-all, whichever you need.

A merged row carries the tag onto an existing account too

If any row in that import was merged into an existing account, that account now also carries the import's tag, even though it is a real, pre-existing contact, not a new one. Cross-check the accounts you are about to bulk-delete against that import's Merged list first, and exclude any that appear there. If the import used the default "Lead" tag, do not use this method at all, searching by "Lead" returns every lead you have. Contact [email protected] instead.

Deleting history never deletes contacts

Single, bulk, and delete-all on Import History only ever remove the log record. Removing the contacts themselves is always a separate, explicit step on the Accounts list.