Definition
OAuth2 SMTP authentication is a way for email clients and apps to authenticate to an SMTP server using OAuth2 tokens rather than a password. It is increasingly required by providers like Microsoft and Google for sending via their infrastructure.
With OAuth2, the user grants access and the client receives a short-lived access token (and refresh token) to send mail, instead of storing a password. This improves security, supports revocable access and integrates with single sign-on and multifactor flows.
For senders, this matters when connecting apps or transactional sending to a mail provider: support OAuth2 where required, handle token refresh, and avoid insecure password-based authentication to maintain access and security.
Was this useful?
Related Glossary Terms
Apple App Password (Email)
An Apple app password is a generated, app-specific password used to sign into an email account through clients that do not support two-factor authentication.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.
DKIM (DomainKeys Identified Mail)
DKIM (DomainKeys Identified Mail) is an email authentication method that uses digital signatures to verify that an email was not tampered with during transit and comes from a authorised domain.
DMARC (Domain-based Message Authentication)
DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication protocol that builds on SPF and DKIM to prevent domain spoofing and provide reporting on authentication failures.
Email API Key Management
Email API key management covers creating, storing, rotating, and revoking API credentials used to connect email platforms, ensuring security while maintaining reliable integration access.
Frequently Asked Questions
It is authenticating to an SMTP server with OAuth2 tokens instead of a password, a modern method increasingly required by major email providers.
OAuth2 is more secure: access is revocable, scoped and integrates with modern sign-in, so providers phase out risky password-based SMTP authentication.
Have users grant access to your app, store and refresh short-lived tokens securely, and connect them to your mail client or sending service that supports OAuth2.