SMTP Error Codes: What Do These Server Responses Mean?

Undecided what an SMTP error code means? You’re not alone. It may be stunning and complicated to see SMTP errors typically, and we wish to get rid of the confusion with a quick-and-easy rationalization.

Under, we’ll clarify every little thing it’s worthwhile to find out about SMTP error codes, together with brief explanations of widespread ones you’ve seemingly seen earlier than.

What’s an SMTP error code?

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

Whereas messages are normally despatched with out situation, completely different server response codes can point out varied issues.

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

Widespread 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. That is normally 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 will occur if the mailbox is locked or will not be routable.
• SMTP 451: This response is shipped when the message merely failed. Usually occasions this isn’t brought on by you, however moderately due to a far-end server drawback.
• SMTP 452: This type of response is shipped again when there isn’t sufficient system storage to ship the message. Your message is deferred till storage opens up and it may possibly 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 title of the mailbox you despatched it to doesn’t exist.
• SMTP 554: It is a very imprecise message failure response that may seek advice from any variety of issues both in your finish or with the recipient server.

There are a number of points that may set off these SMTP server responses, and also you’re not anticipated to know the right way to deal with all of them. SendGrid’s wonderful assist employees is right here that can assist you determine what went improper 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 ideas for correcting any issues.

Sending electronic mail includes a number of computer systems speaking with one another by means of a course of name Easy Message Switch Protocol (SMTP). SendGrid features as an SMTP relay service to ship billions of selling and transactional emails each month.

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