Support for Microsoft Exchange MIME-encoded emails - Reply by email

Overview:

Many enterprise organizations use Microsoft Exchange server. GitLab should support parsing the default Exchange 2010, 2013 MIME-encoded emails. Currently only plain-text is supported and HTML messages must be sent with a plain-text section Microsoft Exchange does not do this by default.

Exchange format types: https://technet.microsoft.com/en-us/library/bb232174(v=exchg.150).aspx

Related: https://gitlab.com/gitlab-org/gitlab-ce/issues/2847

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Requested by customer: https://gitlab.zendesk.com/agent/tickets/26148 and https://gitlab.zendesk.com/agent/tickets/33322