Mail Sheild interfering with iCloud syncing in Apple Mail app

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Hi guys. I've got two Machines that started having trouble syncing with my iCloud account using Apple mail when the Mail Shield is enabled. Couldn't figure out what it was for a few days. Basically Mail will hang going to fetch messages/move items to trash etc. Console indicates IMAP problems and such. Quitting and restarting the app a couple of times will sometimes get it to sync, but then Mail will get unstable and crash eventually as a result when it gets stuck trying to fetch new mail. It's happening on 2 different Macs on two different networks. Most likely related to the release of OS X 10.10.3. Disabling the Mail Shield fixes the issue immediately. If you're already aware of this issue, let me know. If not and you want console messages let me know.

Thanks

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I too have been chasing down intermittent and sporadic Apple Mail via iCloud problems for several weeks.  Sent messages disappear from Mailbox and then reappear at later date.  Mail application frequently stalls at Downloading Messages or Checking for Mail.  Mail application frequently crashes.  One day the system works perfectly and without any delays, and the next day it is totally constipated.  Got wind tonight of a possible Avast connection.  Initial experimentation has shown that disabling the Avast Mail Shield and restarting Mail gets things running smoothly again.  Will need to due more trial cases as my time and patience allow. 

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Please see my post.

https://forum.avast.com/index.php?topic=182201.0