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https://konkretor.com/2019/10/15/exchange-2010-2013-activesync-devices-are-not-able-to-send-e-mails-sporadically-e-mails-with-attachment-and-long-conversation-history/
Exchange 2010/2013 - ActiveSync devices are not able to send e-mails sporadically. E-mails with attachment and long conversation history