According to a thread on the Apple Support Community started on Monday, a number of emails sent to Apple addresses have failed to arrive, with forum members discovering that the issue lies with messages originating from Comcast and Roadrunner domains. Outgoing messages are currently unaffected.
Users are reporting that the Mac Mail, iPhone and online clients are all affected, including those not yet transitioned to iCloud.
Some claim that because affected ISPs are spread across the country and problems are contained to only Comcast and Roadrunner accounts, the issue could be with Apple's servers. Community reports also note that Apple support representatives are aware of the problem, though the company has not yet acknowledged culpability.
Forum members have found that forwarding incoming mail to another account may be a temporary fix, though the workaround is not a universal solution.
The issues comes less than two months after AppleInsider reported MobileMe users were having trouble migrating their accounts and syncing data with iCloud in October.