Configure "Send mail as" In Gmail For Personal Outlook.com Emails
An SMTP relay service to restore Gmail's "Send mail as" functionality for your Outlook.com account after Microsoft's basic authentication deprecation on September 16, 2024.
The Issue
As of September 16, 2024, Microsoft has discontinued basic authentication for personal Outlook.com accounts. This change affects Gmail's "Send mail as" feature, which relies on basic SMTP authentication. Since Gmail hasn't updated their SMTP integration, users can no longer send emails through Outlook.com accounts via Gmail. Notably, attempts to connect to the Outlook.com SMTP server smtp-mail.outlook.com results in the following error:
Authentication failed. Please check your username/password. Server returned error: "334 VXNlcm5hbWU6 334 UGFzc3dvcmQ6 535 5.7.139 Authentication unsuccessful, basic authentication is disabled. [AS4P251CA0014.EURP251.PROD.OUTLOOK.COM 2024-10-26T21:19:04.955Z 08DCF55F2D078725] , code: 535"
The Solution
This is a secure bridging service that enables Gmail to communicate seamlessly with Microsoft's modern authentication systems. It functions as an SMTP proxy that:
- Accepts incoming email traffic from Gmail using a compatible SMTP server
- Securely handles the authentication and transmission process using TLS encryption
- Forwards your emails through Microsoft's Graph API using their sendMail endpoint
The service maintains end-to-end security by using encrypted HTTPS for Microsoft communications and TLS for Gmail connections. This ensures your email content remains protected and tamper-proof throughout transmission, while adhering to both Gmail's and Microsoft's security protocols. This is provided as a free service for personal use and the author strongly encourages self-hosting if this functionality is critical to you.
The only permission this service requests is Mail.Send, which is required to send emails on your behalf. Your email credentials are never stored or logged and no access is granted to your contacts or inbox. Revoke this limited permission at any time via https://account.microsoft.com/privacy/app-access.
Sign in with MicrosoftSecure authentication through Microsoft's official OAuth 2.0 flow