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SMTP Error Codes: What Do These Server Responses Mean?

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Not positive what an SMTP error code means? You’re not alone. It will be surprising and complicated to see SMTP errors typically, and we need to get rid of the confusion with a quick-and-easy clarification.

Below, we’ll clarify every little thing you could find out about SMTP error codes, together with quick explanations of frequent ones you’ve probably seen earlier than.

What is an SMTP error code?

Within the SMTP course of, messages are relayed from one laptop to a different by way of SMTP servers. SMTP servers ship response codes that point out what has occurred to messages.

While messages are often despatched with out subject, totally different server response codes can point out numerous issues.

Below are a handful of SMTP server response codes that we’ve compiled that you just would possibly see when sending emails.

Common SMTP error codes

  • SMTP 250: This SMTP server response merely means every little thing went properly and your message was delivered to the recipient server.
  • SMTP 421: Your message was quickly deferred by the recipient server. This is often a results of too many connections in a brief timeframe or too many messages.
  • SMTP 450: Your message was not delivered as a result of the opposite person mailbox was not out there. This can occur if the mailbox is locked or is just not routable.
  • SMTP 451: This response is distributed when the message merely failed. Often instances this isn’t brought on by you, however moderately due to a far-end server drawback.
  • SMTP 452: This sort of response is distributed again when there isn’t sufficient system storage to ship the message. Your message is deferred till storage opens up and it might then be delivered.
  • SMTP550: The message has failed as a result of the opposite person’s mailbox is unavailable or as a result of the recipient server rejected your message.
  • SMTP 551: The mailbox your message was meant for doesn’t exist on the recipient server.
  • SMTP 552: The mailbox your message was despatched to doesn’t have sufficient storage to simply accept your message.
  • SMTP 553: Your message was not delivered as a result of the identify of the mailbox you despatched it to doesn’t exist.
  • SMTP 554: This is a really imprecise message failure response that may confer with any variety of issues both in your finish or with the recipient server.

There are quite a lot of points that may set off these SMTP server responses, and also you’re not anticipated to know learn how to deal with all of them. SendGrid’s wonderful help employees is right here that can assist you determine what went fallacious and what you are able to do to right it.

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To study extra about these and different SMTP server responses, learn our Knowledge Base article. The article supplies examples of all these responses in addition to presents recommendations for correcting any issues.

Sending email entails a number of computer systems speaking with one another by a course of name Simple Message Transfer Protocol (SMTP). SendGrid features as an SMTP relay service to ship billions of promoting and transactional emails each month.

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