Secure File Circumventing Corporate Security

• Privacy Concerns: Mimecast Secure Folders require recipients to sign up, which may infringe on their privacy if not managed by the recipient’s consent.
• Corporate Compliance Issues: This can bypass existing corporate file screening and scanning processes allowing employees to access files they should never be able to receive. 
• These 'links' are often stripped out by other mail filters leaving the files unavailable whereas they would have been if sent as a normal attachment. 

Poor Support

• Inadequate Customer Service: Many users report that support is slow and unhelpful. Issues reported can take days or weeks to resolve.
• Lack of Expertise: The support team may not always have the necessary expertise, leading to prolonged troubleshooting times and unsatisfactory outcomes.

Greylisting Practices

• Outdated Technique: Greylisting involves temporarily rejecting emails from unknown senders based on their previous activity. While it can help reduce spam, it is rarely used in modern email security practices.
• Impact on Legitimate Senders: This practice can significantly delay or even block legitimate emails, placing an unnecessary burden on the sender's system and causing delays for recipients.

Excessive Blocking Policies

• Overblocking of Attachments: Mimecast has been known to overblock common attachments such as GPG keys and signatures. This can disrupt legitimate communications without providing clear justification.
• Customer Complaints: Numerous complaints have surfaced regarding the blocking of important files, causing frustration among users.

Controversies and Drama

Privacy and Security Concerns

• Data Handling: There are concerns about how Mimecast handles user data, particularly in terms of privacy. The requirement for sign-ups could potentially expose sensitive information.
• Transparency Issues: Lack of transparency around their security measures has led to mistrust among users who feel their data is not adequately protected.

Corporate Client Conflicts

• Misalignment with Corporate Policies: Large corporations may find Mimecast's practices incompatible with their internal security protocols, leading to frequent conflicts and non-compliance issues.
• Legal Scrutiny: Some legal experts have raised questions about the implications of using third-party services for sensitive corporate communications.

Summary

Mimecast’s reputation is marred by concerns over privacy, inadequate support, outdated greylisting practices, and overly restrictive attachment policies. These factors, combined with reported conflicts between Mimecast's methods and corporate security standards, contribute to its poor standing among users and clients.