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 properly configured authentication for your mail server;
  • VPN connection;
  • Non-alphanumeric characters in username;
  • Recipient uses port 25 while connecting to your server;
  • 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 port 25 can be blocked by some Internet service providers;
  • 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.
Rate this article about "Error 503"

User Rating: 4 / 5 (5)

Other useful articles

Popular in Our Blog

Try SendPulse SMTP for free