When exporting a contact source or an email report, the actual file downloaded contains less contacts than expected. For example, a database which has 500,000 contacts only shows 33,000 contacts in the file. In each subsequent attempt, the 500,000 contacts are not downloaded.
Resolving the problem
In these cases, it is best to use SFTP (File Transfer Protocol) instead.
To send your file from the Acoustic Campaign to SFTP, navigate to the: Export Files folder.
Then you need to check the box to the left of your file name and click on the Export to sFTP.
This will move the file to the SFTP server and once done, you can then use your SFTP Client to access the server and download the complete file which will contain all of the contacts.