Note: https://www.us-cert.gov/ncas/current-activity/2019/06/13/Exim-Releases-Security-Patches

That said, I don't believe we've been affected.
Not in a bad way at least, because:
- we run exim as non-root and capabilities dropped
- we run exim in a private Docker network with known trusted relayers
(Synapse and mxisd)