Mimecast Anti-Spoofing Header Lockout. How to bypass.

There are 2 ways to bypass anti-spoofing.

Create a New Anti-Spoofing Policy

• Write a Policy Narrative indicating the intention of the policy

• Set Take No Action

• Set Addresses Based On Both

• Set Applies From

• Set Applies To

• Enable Policy Override

• Input Source IP Ranges

Create a New Anti-Spoofing SPF Based Bypass Policy

• Write a Policy Narrative indicating the intention of the policy

• Set Enable Bypass

• Input SPF record of sender

• Set Applies from

• Set Applies to

We recommend using the most specific bypasses possible and avoiding large bypasses completely.

For example: the most specific bypass would be to create a new anit-spoofing policy scoped using a single email address to another single email address set to take no action and using only 1 /32 IP address.

The most general bypass is highly dangerous and is set from everyone to everyone take no action with 0 IPs listed and policy override checked. This would effectively turn off your anti-spoofing for all incoming mail.

Anti-spoofing bypasses can be complex and should not be tampered with without a full understanding of how they work. We have seen many instances where anti-spoofing is  fully disabled intentionally or unintentionally in an attempt to allow certain mail through and that creates a major vulnerability. Feel free to reach out to us for help.