iCloud Postmaster(y) page

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Market share and history of MBP

iCloud is an Apple service that has been created to replace MobileMe (@mac.com and @me.com addresses) and was released on October 12, 2021. In May 2022, iCloud was having over 850 million users, which represents the exact same number of icloud.com email addresses.

Anti-Spam Measures

To safeguard iCloud Email against spam, Apple employs sophisticated techniques such as trend analysis, dynamic lists, and other technologies to automatically detect and block junk mail before it enters users' inboxes. Apple utilizes Proofpoint, which analyzes messages to identify spam fingerprints and blocklists associated IPs. Spamhaus blacklistings will also cause immediate rejection messages.

Feedback Loop

iCloud Mail does not provide a feedback loop (FBL) service. However, it encourages bulk email senders to actively manage their subscriber lists to ensure that only engaged recipients continue to receive emails.

iCloud Postmaster Technical & SMTP Tweaks

iCloud has the following 2 MX records with the same priority.
mx01.mail.icloud.com.
mx02.mail.icloud.com.

iCloud has not published about the number of messages that can be sent per connection or number of concurrent connections it accepts. iCloud can be slow in accepting messages and we recommend opening concurrent connections for high throughput.

iCloud recommends authenticating messages with SPF, DKIM and DMARC. iCloud also supports BIMI and requires a Verified Mail Certificate (VMC).

Common Error SMTP Messages

421 4.7.1 Messages to xxxx@mac.com deferred due to excessive volume. Try again later - https://support.apple.com/en-us/HT204137.

The delivery is deferred due to a particular recipient that has exceeded the number of emails that iCloud has allowed the recipient to accept in a time period. It happens when you are sending messages to a seed address.

550 5.1.1 xxxx@icloud.com: user does not exist
The bounce message refers to a nonexistent recipient. Such recipients should be treated as hard bounces, not retried, and removed immediately from the mailing list after the first occurrence.

550 5.1.1 <xxxx@icloud.com>: inactive email address
The bounce message refers to an inactive recipient. ICloud allows users to temporarily deactivate an email address. Such recipients should be marked as soft bounce and suppressed after 3-5 consecutive occurrences over a period of 4-6 weeks.

xxxx@icloud.com: user is overquota
The bounce message refers to a recipient that’s running out of disk space. Such recipients should be marked as soft bounce and suppressed after 3-5 consecutive occurrences over a period of 4-6 weeks.

554 5.7.1 [HME1] This message was blocked for failing both SPF and DKIM authentication checks. See https://support.apple.com/en-us/HT204137 for mailing best practices
The bounce message is related to the sender, not the recipient. The sender domain does not authenticate itself with both SPF and DKIM. We recommend setting up a valid SPF record and enabling DKIM.

554 5.7.1 Your message was rejected due to example.com's DMARC policy. See https://support.apple.com/en-us/HT204137 for info
iCloud has rejected the message because your domain has failed DMARC authentication and has a DMARC reject policy. Make sure you have SPF and (or) DKIM authentication enabled and the domain is aligned with the header. From.

550 5.7.0 Blocked - see https://support.proofpoint.com/dnsbl-lookup.cgi?ip=X.X.X.X
The bounce message indicates that the IP is listed on Proofpoint. After the IP is mitigated, it may take a while for the delivery to be fully restored.

1. 550 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT20413
2. 550 5.7.1 Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137
3. 554 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137 # bounces seem to be domain/content related, not IP related. # FROM 552 5.2.2
4. 554 5.7.1 [HM08] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137

These 4 bounce reasons refer to the sender/ IP reputation and are unrelated to the recipient address.

550 5.7.1 Mail from IP x.x.x.x was rejected due to listing in Spamhaus SBL. For details please see http://www.spamhaus.org/query/bl?ip=x.x.x.x
The sending IP is listed on Spamhaus SBL. You can check and mitigate IPs at https://check.spamhaus.org/. After the IP is mitigated, it may take a while for the delivery to be fully restored.