iCloud
iCloud provides Apple customers with free email accounts. Users can also link their custom domains to it. Their postmaster includes some basic deliverability recommendations, but troubleshooting requires contacting their Postmaster team.
Domains
icloud.com · me.com · mac.com
Codes
- 421↑
421 4.7.0 me.com Error: too many errors
421 4.7.1 Messages to example@icloud.com deferred due to excessive volume. Try again later - https://support.apple.com/en-us/HT204137
The email address is currently receiving an email at a high rate. Sending email in the future will most likely be successful.
- 451↑
451 4.7.1 Service unavailable - try again later
Messages are not being accepted right now. You may usually see this for sends happening at the "top of the hour" when many senders around the world are also sending aggressively to Apple.
- 550↑
550 5.1.1 <example@icloud.com>: user does not exist
This mailbox does not exist at Apple. Check to make sure there are no typos with the address.
550 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137
Apple Mail is blocking the email because of an email filter policy on their end. If you're unsure of the source of this issue, and following Apple's suggested best practices, you can contact Apple's postmaster team with mail logs for delivery support.
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
The sent message failed the DMARC policy for the sending domain. If the sending domain has a reject policy set for DMARC, the message must pass DKIM or have SPF aligned to the domain with a custom Return-Path. To resolve this, you'll need to contact your email service provider to see how to send a message that passes DMARC support.
550 5.7.1 Your email was rejected due to having a domain present in the Spamhaus DBL -- see https://www.spamhaus.org/dbl/
Apple Mail checks all URLs in your message content against the public block list Spamhaus. Spamhaus is a very reputable block list with few false-positive listings. You must cooperate with Spamhaus volunteers to resolve the listing. Remember that even once the listing is removed, it may take receivers up to 24 hours to refresh their cache and to see delivery resume.
- 554↑
554 5.7.1 <example@icloud.com>: Relay access denied
554 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137
Apple Mail is blocking the email because of an email filter policy on their end. If this is happening for a specific recipient, ask them to save the From address for the message as an iCloud contact, specifically marking them as a "VIP" there. This VIP status should at least temporarily override the block. If you're following Apple's suggested best practices, you can also contact Apple's postmaster team with mail logs for delivery support.