4.8.4. Error "550 5.7.1 This message was blocked because its content presents a potential security issue"

This error may occur when sending emails with attachments that contain malicious code. You can check for malicious code in attachments, for example, using the VirusTotal service.

If the attachments are indeed infected, the following are possible solutions to the problem:

• Try cleaning the forwarded files with antivirus software and resend the email with them.
• Upload files to any file sharing service and send only the link to the file in the email instead of the file itself.