I encountered the below error message when trying to send an email to an email address (xxxx@gmail.com). This happens when there is a Contact record in CRM where the Full Name field is same as email address.
Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: Contact With Id = 00000000-0000-0000-0000-000000000000 Does Not ExistDetail:
<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">
<ActivityId>a34306e2-87fd-4b06-add4-fe877dd1a3a5</ActivityId>
<ErrorCode>-2147220969</ErrorCode>
<ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
<Message>Contact With Id = 00000000-0000-0000-0000-000000000000 Does Not Exist</Message>
<Timestamp>2019-11-14T08:43:44.8100292Z</Timestamp>
<ExceptionSource i:nil="true" />
<InnerFault i:nil="true" />
<OriginalException i:nil="true" />
<TraceText i:nil="true" />
</OrganizationServiceFault>
Contact and Email page image: