Dec 03, 2019 · The Mimecast Secure Email Gateway checks messages that are sent from each account. If the sending domain doesn't match a domain listed as internal to the account, it will then check the TXT record of the sending domain for the presence of the DNS Authorization Code. Mimecast cloud cybersecurity services for email, data, and web provides your organization with archiving and continuity needed to prevent compromise. What you do is important - Secure your email Protect your organization from spam, malware, ransomware, and phishing attacks. Mimecast safeguards employee communication and reduces risk with targeted threat protection, data leak prevention, and enforced email security controls. Office 365 requires an added layer of protection. Basic Mimecast Guide. A basic mimecast guide. Mimecast is a cloud based email filtering and archiving service. Email security is a vital part of many businesses, and Mimecast offers users added security against threats such as viruses and phishing, as well as reducing spam. We use Mimecast for both user training and email management. The cloud-based email management system protects email data and employees from spam, malware, phishing, and targeted attacks. It works very well and has provided a lot of value to our IT Security. We are very pleased with its capabilities and its almost magical capabilities. Mimecast DMARC Analyzer can be used to generate DMARC reports containing detailed information about who is sending email on your behalf. How SPF authentication works The SPF TXT record is a DNS record that helps prevent spoofing and phishing by verifying the domain name from which email messages are sent. Once 25 hops has been reached, the email is rejected. Investigate the email addresses in the communication pairs, to see what forwarders are configured on the mail servers. 554: Maximum email size exceeded: The email size either exceeds an Email Size Limits policy, or is larger than Mimecast service limit.