An increasing number of iCloud users is registering complaints of facing Gmail too many rejections issue. This latest issue comes after March 11 outage that hit the App Store and the iTunes lasting for over 11 hours.

"For the last week I've experience [sic] problems getting mail on my .mac/.me/.icloud email account.  It's [sic] seems to be exclusive to Gmail account emails being sent to me.  Co-workers are experiencing similar issues in totally separate scenarios, so I know it's not isolated to me." iCloud user

Gmail "too many rejections" error:

The latest issue that iCloud users are facing is preventing the iCloud.com and me.com email addresses from receiving Gmail messages. The extended delays in mail reception goes over few hours and even days in some cases. Registered in Apple's discussion forums, the increasing number of complaints of this Gmail error indicates some serious issue.

According to sources and discussion threads, it is evident that Apple servers are rejecting Gmail messages since last week for some reason. The reason is so far unknown but it is being said that engineers at Cupertino are working hard to tackle the issue at the earliest.

Users experiencing the delay and other mail related issues are receiving this following pop up error message:

451 4.5.3 Too many rejections; try again later.

If you too are experiencing this issue, do call Apple at 800 275 2273 to report the iCloud mail issues. It is recommended that you make this call and report the issue as engineers are trying to know the cause with as much of information coming from users as possible to find the fix.

"I'm on the phone now with a senior advisor now trying to trouble shoot it.  Seems like this is news to them, they keep researching and putting me on hold.  If I have any progress I'll post here."

- Source: Apple Discussion Threads