Overview

This article addresses August 2025 issues where Mimecast is unexpectedly blocking legitimate Salesforce MTA/email IP addresses due to Invaluement RBL/DNSBL listing. This can lead to disruption in services relying on Salesforce for email delivery.

Understanding the Issue

Mimecast utilizes various threat intelligence feeds, including Invaluement RBL/DNSBL, to identify and block potentially malicious or spammy IP addresses. Occasionally, a legitimate IP address, such as one used by Salesforce, may be incorrectly flagged by these feeds. When Mimecast's Invaluement filter is active and the Salesforce IP is listed, emails originating from that IP will be blocked.

Symptoms

• Salesforce-generated emails are not being delivered to recipients in your organization

• Salesforce email logs showing a 550 error with the details of Invaluement RBL listing - see below

• Mimecast bounced messages or rejected emails indicating a block due to Invaluement RBL listing

Example DSN in Salesforce email logs:

550 sip.invaluement.mimecast.org Blocked by ivmSIP and/or ivmSIP/24 - see https://www.invaluement.com/lookup/?item=X.X.X.X. - https://community.mimecast.com/docs/DOC-1369#550 [abQHp0JQNuyijnD4wtW_xy.us000]