Unsure what an SMTP error code means? You’re not alone. It may be surprising and complicated to see SMTP errors generally, and we need to eradicate the confusion with a quick-and-easy rationalization.

Beneath, we’ll clarify all the pieces you have to find out about SMTP error codes, together with quick explanations of widespread ones you’ve probably seen earlier than.

What’s an SMTP error code?

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

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

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

Widespread SMTP error codes

• SMTP 250: This SMTP server response merely means all the pieces went effectively 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 accessible. This could occur if the mailbox is locked or is just not routable.
• SMTP 451: This response is shipped when the message merely failed. Typically occasions this isn’t attributable to you, however somewhat due to a far-end server drawback.
• SMTP 452: This sort 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 will 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 supposed for doesn’t exist on the recipient server.
• SMTP 552: The mailbox your message was despatched to doesn’t have sufficient storage to just 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 can be 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 deal with all of them. SendGrid’s superb help workers is right here that can assist you work out what went flawed 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 Information Base article. The article supplies examples of all these responses in addition to provides solutions for correcting any issues.

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

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