Got this error message this morning when I’m trying to send email via Microsoft Outlook. “ Undeliverable… 503 Valid RCPT Command Must Precede DATA “

Refer below for the actual error message:

The most common reason is incorrect configuration of mail client. To solve this problem just configure your email client to the SMTP server.

Here’s how I quickly fix th error in outlook:

Go to Tools > Account Setting >> Select the email account & click Change >> More Settings >> Outgoing Server >> Tick My outgoing server (SMTP) requires authentication.

503 Valid RCPT Command Must Precede DATA problem solved.

That’s all. kthnkxbye!