If someone unsubscribes in Gmail, can I email them from a different subdomain?

Hi! In Gmail, a “built-in” unsubscribe click is generally list/message-specific (it triggers whatever your List-Unsubscribe for that particular sender/list points to), so you can keep someone subscribed to other truly separate client programs/subdomains if they separately opted in to those—but you should not treat a Gmail unsubscribe as something to “work around” by simply switching subdomains for the same program, and you should design your suppression rules to match what the recipient reasonably intended.

A practical way to handle it (good for both compliance and deliverability) is:

• Suppress at the program level by default: If they unsubscribed from Client A on clienta.example.com, stop all marketing for Client A (even if Client A could technically send from another subdomain later). This avoids looking like you’re evading an opt-out, which is a fast path to spam complaints and reputation damage.
• Only keep them mailable for Client B / Client C if you have separate consent: If your programs are truly independent (different brands, different sign-up source, clear “who is emailing me”), it’s reasonable to treat unsubscribes as not automatically global across other client subdomains.
• Offer (and honor) a “global unsubscribe” option anyway: Even if Gmail’s one-click unsubscribe is list-specific, many recipients mean “stop emailing me from you.” A simple checkbox or link like “Unsubscribe from all programs” reduces complaints and protects deliverability.

A few deliverability/compliance notes that matter here:

• Make the “From” identity crystal clear per client (brand name + consistent sending domain) so recipients understand what they’re unsubscribing from.
• Keep suppression lists partitioned by client/program, but also maintain a global suppression layer you can apply when someone explicitly opts out of everything, complains, or you detect clear negative engagement (repeated deletes/spam complaints).
• Process unsubscribes fast. Google explicitly recommends honoring one-click unsubscribes within about 48 hours for healthier engagement and fewer spam reports (and it aligns well with most ESP expectations).
• Don’t email people who opted out of a given sender/program, even if another subdomain could technically deliver—regulators and mailbox providers tend to look at intent and user experience, not just DNS boundaries.

If you tell me whether these subdomains represent (1) separate legal entities/brands vs (2) one parent brand with multiple products, I can suggest the cleanest suppression model (program-only vs “global by default + opt back in per program”) for the least risk.