Every email service provider has to deal with this from time to time, but well-designed email operations and infrastructure should generally limit the impact to a small subset of customers - usually, especially with a known high-volume sender, Spamhaus will list as narrow of a range as possible to prevent false positives.

The fact that this applies so broadly implies that Intercom may need to rethink some of the details of their email operations, and/or beef up their anti-spam enforcement efforts.

As an aside, it appears Intercom uses Mailgun with dedicated IPs, judging from recent samples.