Can a compromised subdomain drag the main domain into spam?

Compromised subdomains can damage parent domain reputation:

Organizational inference where providers conclude that subdomain problems reflect poor practices at the corporate level.

Spillover filtering where increased scrutiny of the subdomain leads to more aggressive filtering of related domains.

Blocklist propagation where severe subdomain issues lead to parent domain or organizational listings.

The damage is not automatic or immediate. Minor subdomain issues typically stay contained. Severe or sustained abuse triggers broader consequences.

Prevention requires monitoring all subdomains, enforcing security on unused subdomains, and having incident response plans for compromised identities.

A compromised subdomain is like a rogue ship flying your colors. Eventually, enough smuggling incidents under your flag bring the whole fleet under suspicion.