Error 503

Have you ever faced Error 503 – Valid RCPT command must precede DATA while sending emails?

Let’s take a closer look at the causes and solutions of this error.

You have not correctly configured authentication for your mail server;
VPN connection;
Non-alphanumeric characters in your username;
The recipient uses port 25 while connecting to your server;
The email address that you send from may differ from the address, seen by a recipient;
Full mailbox.

Properly authenticate SMTP connection;
Ask the recipient to disconnect VPN;
Remove non-alphanumeric characters from your email account if there are any (! @ # & ( ) – [ { } ] : ; ', ? / *);
Change the port from 25 to 26, as some Internet service providers can block port 25;
Make sure the inbox is not full, otherwise contact your provider and ask to increase the limits;
Make certain that your “From” field address seen by the recipient is the same one that you send from.

Last Updated: 27.01.2020