The Exclaimer Cloud service addresses a number of IP addresses. If you use third party anti-spam or virus vendors such as Mimecast (or other smart hosts), you may need to whitelist these addresses. This ensures that the third-party vendor accepts the SMTP connection from Exclaimer Cloud, instead of rejecting it (which results in message delivery failure).
IP addresses used by Exclaimer Cloud
Note: Please provide your third-party vendors with this list, so they can update/add entries as needed.