| Feature | Gmail | Outlook.com | Yahoo! Mail | | --- | --- | --- | --- | | Market Share (2021) | 44.3% | 23.6% | 12.8% | | Number of Users (2021) | 1.5 billion | 400 million | 225 million | | TXT Records | SPF, site verification | SPF, site verification | SPF, site verification | | Security Features | 2FA, password protection, phishing detection | 2FA, password protection, threat protection | 2FA, password protection, account security |