Illingworth says subdomains held across 1.8M sends

Richard Illingworth says a client of his sent 1.8 million cold emails in six weeks off 5,000 accounts built on infrastructure most senders are told to avoid. Every account was an official Google account, and each root domain carried 10 subdomains. Nothing ever went out from the root.

The reported outcome after six weeks and 1.8 million sends is 99.7% average inbox health across all 5,000 accounts, a 0.6% bounce rate and 2,000+ opportunities from that one build. Illingworth says the same team now runs roughly 10,000 accounts built the same way, and that none of their root domains has sent a cold email.

The rule the whole thing rests on

The standard warning is that Google treats a root and its subdomains as one family, so one flag takes the rest down with it. That is why the default advice is a separate domain for every couple of inboxes. Illingworth's argument is narrower than it first sounds. He says the family effect only kicks in when the root itself is the sender, and that keeping the root silent means a flagged subdomain burns alone and you cut that one off.

In a separate post he says his team tested the question across 30 million sends and found subdomains performed the same as separate domains. He lists the rules plainly. The root never sends a cold email, only the subdomains do. If the root sends and gets flagged, everything on it goes down. He adds that he does not sell domains, so the choice makes no difference to him.

Richard Illingworth

@RCIllingworth

X

subdomains performed the SAME as separate domains.

What to hold back on

These are one provider's own client numbers, self reported, with no independent view of the sending list, the offer or how opportunities were counted. The 2,000+ opportunities figure in particular is the softest number in the post, since opportunity definitions vary wildly between teams. Inbox health and bounce rate are at least mechanical measures, but they come from the same internal monitoring Illingworth is offering to wire prospects into.

For people sending, the practical read is that the claimed result is conditional, not general. It depends entirely on the root staying silent forever, across every team member, every tool and every campaign. One stray send from the root, in Illingworth's own framing, is the thing that puts every subdomain under it at risk. That is a process problem, not a deliverability trick, and it gets harder to enforce as the account count climbs. He has previously published his broader infrastructure blueprint for high volume sending.

Richard Illingworth

@RCIllingworth

X

subdomains only burn together when the root domain is the one doing the sending.