Summary of impact:
On Monday 26th April 2021 at approx. 11:00 UTC, Apple experienced a partial outage with their mailing system. This outage had a knock on effect meaning some emails sent to icloud.com, me.com and mac.com email addresses may have incorrectly hard bounced, been subsequently suppressed in customer accounts and added to the Global Suppression List (GSL). Apple resolved the issue and normal services resumed at approx. 16:30 UTC.
During the stated time period, Apple experienced a problem which led to around 17% of emails to valid email addresses hard bouncing. The bounce error received was:
550 5.1.1 <*>: user lookup success but no user record found. As this is a hard bounce error, it caused email addresses to be suppressed. In addition, these email addresses were inadvertently added to the Global Suppression List (GSL). This meant if customers ran the GSL and applied hard bounce suppressions, these ‘valid’ email addresses would’ve been unsubscribed.
Once we were notified about the problem, the timeline for resolving the issue was:
We’re going to conduct some work to understand the measures we could introduce to minimize the impact we experience when mailbox providers have issues like this.