iPhones are periodically ceasing to synchronize with Exchange Server 2007 (all updates). Phone will operate fine for a period of time, then stop receiving mail. Users get "Cannot Send Mail. An error occurred while delivering this message" when trying to send email. Confirmed that internet service is not dropping. Later, a barrage of messages will rush in for no apparent reason. Issue MAY be related to the recent renewal of ssl certificate. Tried different phones, different mailboxes, removing/adding mailbox. Problem occurs on Wi-Fi as well as LTE network. Tried removing partnerships in EMC.