A few weeks ago it happens very unusual error with the e-mails received by the Microsoft Exchange Server 2013. All e-mails received from one specific e-mail address, which belongs to one of our vendors, are completely garbled.
Every e-mail is composed of several parts and contains the XML code. One day, suddenly, all e-mails are converted to plain text and the attachments are missing. When this anomaly appears, it affected all users.