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.

Causes of Error 503:

  • 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.

How to avoid Error 503:

  • 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.
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