[Exim] Yahoo and Juno mail problems

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I have an EXIM mail server configured using Mysql with only virtual
users. Most situations work just fine, but I seem to be having a large
number of mail messages that are not able to reach Yahoo and Juno
accounts. Some times I can get mail through and some times I cannot. Is
there any known issue with these mail services? Do I have something set
up incorrectly? Any help would be appreciated.
Thanks
Van
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