Within the last 48 hours, 3 customers and 1 employee of our company have received emails that mimic our E-commerce transaction receipt email very closely. The email is off very slightly but there's an attachment - extension ending is .MHT. The only thing these 4 individuals have in common that I know of is our company.
Has anyone seen this sort of email behavior recently and any ideas where to dig to root it out? I'm quite sure it's either malware, ransomware, or a phishing attempt.
Thanks in advance for any help.