Administration - Frequently Asked Questions

For a comprehensive list of all Mimecast's regional IP addresses, see the Mimecast Data Centers and URLs page. 

• Only US customers with CUSA account codes need to make these changes.
• CUSA customers should only refer to the United States of America grid IP addresses. United States of America (B grid) IPs are not relevant.

Q:	Why is Mimecast making this change?
A:	Mimecast is retiring all leased IPv4 address ranges and migrating to directly owned ranges. This will allow for improved platform performance and availability.
Q:	When do I need to make these changes?
A:	Customers who route their email through our German and Australian data centers will need to make this change before October 31, 2022. Customers who route their email through our US-A center will need to make this change before February 28, 2023. (Extended to September 25th, 2023)
Q:	What are the port numbers Mimecast uses?
A:	SMTP port 25 LDAP port 636 LDAP port 389
Q:	How do I test my connection?
A:	To test your SMTP connection: Log in to the Mimecast Administration Console. Navigate to Policies | Gateway Policies | Definitions | Delivery Routes. Select the definition you wish to test.  Click Test Connection - Strict TLS or Test Connection - Relaxed TLS. To test your directory connector:  Navigate to Mimecast Administration | Users & Groups | Directory Synchronization.  Select the directory connector.  Click Test Connection.
Q:	If I need assistance who do I speak to?
A:	If you need further assistance, please open a Support case in the Mimecast Community.
Q:	If I have IP addresses not on the list provided, do I delete them now?
A:	No. There will be a double-run period for new and deprecated IP addresses. Further notification will be sent when non-listed IPs can be deleted.
Q:	I have deleted the IP address ranges, and now I am not receiving emails.
A:	Roll back any deletions and do not make any further deletions until explicitly notified by Mimecast.
Q:	Can Mimecast make these changes for me?
A:	No. Mimecast cannot make these changes for you. They will need to be completed by on-site resources.
Q:	I look after multiple customers. Do I need to make these changes on all of them?
A:	No. Mimecast has had these IP ranges listed for a few years and is now only contacting customers that we cannot connect to. Not all customers are affected by this.
Q:	Some of my customers don't need changes- why is that?
A:	Either the customer was provisioned after the Knowledge Base articles were updated with new IP ranges, or the customer does not have any IP range restrictions on inbound firewall policies.
Q:	Do I need to let Mimecast know once I have made the changes?
A:	No. Mimecast will have visibility of any changes made via regular connectivity reports.
Q:	What happens if I don't make the changes?
A:	If you currently restrict inbound connectivity to advertise Mimecast IP ranges and do not adjust firewall policies to allow the updated IP ranges, Mimecast services relying on inbound connectivity to your environment may cease to work when leased IP ranges are deprecated.