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Apple SMTP Error Codes and Bounce Messages

Apple provides iCloud Mail for icloud.com, me.com and mac.com addresses. There is little self-service tooling, so anything beyond following its published guidance needs a message to its postmaster team.

Codes on record
5
Responses
10
Domains
icloud.com, me.com, mac.com

Postmaster & documentation

421451550552554

SMTP 4212 responses

Medium severityView all
4.7.0

smtp;421 4.7.0 me.com Error: too many errors

4.7.1Medium severity

smtp;421 4.7.1 Messages to [email protected] deferred due to excessive volume. Try again later - https://support.apple.com/en-us/HT204137

A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 421 across every provider

SMTP 4511 response

Low severityView all
4.7.1Low severity

smtp;451 4.7.1 Service unavailable - try again later

A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 451 across every provider

SMTP 5504 responses

Critical severityView all
5.1.1

smtp;550 5.1.1 <[email protected]>: user does not exist

5.7.1

smtp;550 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137

5.7.1-2High severity

smtp;550 5.7.1 Your message was rejected due to example.com’s DMARC policy. See https://support.apple.com/en-us/HT204137 for info

5.7.1-3Critical severity

smtp;550 5.7.1 Your email was rejected due to having a domain present in the Spamhaus DBL -- see https://www.spamhaus.org/dbl/

A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 550 across every provider

SMTP 5521 response

View all
5.2.2

smtp;552 5.2.2 <[email protected]>: user is overquota

A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 552 across every provider

SMTP 5542 responses

Medium severityView all
5.7.1

smtp;554 5.7.1 <[email protected]>: Relay access denied

5.7.1Medium severity

smtp;554 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137

A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 554 across every provider

Apple bounce questions

›Why is Apple bouncing my email?

Apple provides iCloud Mail for icloud.com, me.com and mac.com addresses. There is little self-service tooling, so anything beyond following its published guidance needs a message to its postmaster team. Match the exact wording of your bounce to one of the 10 responses on this page to find the specific reason and fix.

›How do I improve deliverability to Apple?

Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes. Apple also publishes postmaster guidance, linked on this page.

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