A "750k Gmail Combolist" is a plain text file containing approximately 750,000 unique pairs of email addresses and passwords harvested from various data breaches, phishing campaigns, or infostealer malware logs.

Short for "combination list," these files are structured as email:password or username:password pairs.

They are often compiled from previous high-profile leaks (e.g., LinkedIn, Dropbox) or freshly harvested "stealer logs" from infected devices. Risks and Legality Illegal File Sharing Risk and Legal Alternatives - InfoSec

Cybercriminals use them for credential stuffing attacks, which exploit the fact that many people reuse the same password across multiple services. Automated tools like OpenBullet or SilverBullet test these thousands of combinations per second to gain unauthorized access to accounts.