RELATED: Why Am I Getting Spam From My Own Email Address? How each provider handles this situation is a bit different. The big email providers, such as Google, Microsoft, Apple, and Yahoo, use something called SPF (Sender Policy Framework), DMARC (Domain-based Message Authentication, Reporting, and Conformance), and DKIM (Domain Keys Identified Mail) to prevent (among other things) people from sending emails from addresses (spoofing) that aren’t theirs. What will happen with your email is entirely dependent on how your email provider’s SMTP server is configured. The client simply sends the email to your provider’s SMTP server (Simple Mail Transfer Protocol server, often called a mail server), and lets the SMTP server decide what to do with your email.
Microsoft Outlook itself, and other email clients like Thunderbird or Apple Mail, don’t do any checking on the email address from which you send. How Email Providers Handle Messages Sent From a Different “From” Address Both of those answers are dependent on who your email provider is.
