Routing Unresolved Google Workspace Recipients to Zoho Mail
Split-delivery design that keeps Google Workspace as primary MX while relaying mail for unrecognised addresses to a Zoho Mail mailbox instead of bouncing it.
01Purpose & Scope
Google Workspace is the domain's primary mail system of record. Today, any message addressed to a recipient that does not exist as a Workspace user is rejected at the SMTP boundary and bounced back to the sender. This document specifies a routing configuration that intercepts only unrecognised / catch-all addresses and relays them to a designated mailbox in Zoho Mail, while all mail addressed to real Workspace users continues to be delivered in Gmail unchanged.
Unrecognized/Catch-allaccount type, and the mail-route definition pointing at Zoho's inbound server.02Current State
MX records for the domain point to Google. Workspace evaluates the recipient against its user/group directory on every inbound message:
| Recipient type | Current behaviour | Desired behaviour |
|---|---|---|
| Existing Workspace user | Delivered to Gmail inbox | No change — Delivered to Gmail inbox |
| Group / alias | Delivered per group settings | No change |
| Non-existent address | Bounced (5xx, NDR to sender) | Relayed to Zoho catch-all mailbox |
| Suspended user / Gmail off | Not covered by Routing settings | No change — requires Default Routing separately |
03Proposed Design
Two Admin Console objects are introduced, both scoped to the top-level organisational unit:
- Mail Route — a new host entry under
Gmail → Hostspointing at Zoho's inbound MX (e.g.mx.zoho.com, region-specific), TLS enforced. - Routing Rule — under
Gmail → Routing, an inbound rule that modifies the route for messages only whenAccount types to affect = Unrecognized/Catch-all, redirecting them to the route created above.
Message flow
04Configuration Steps
4.1 — Add the Zoho mail route
Admin console → Apps → Google Workspace → Gmail → Hosts
# Add Route
Host name/IP: mx.zoho.com # or region: mx.zoho.eu / mx.zoho.in
Port: 25
Security: Require TLS (recommended)4.2 — Create the catch-all routing rule
Admin console → Apps → Google Workspace → Gmail → Routing → Configure / Add another rule
| Field | Value |
|---|---|
| Email messages to affect | Inbound |
| Action | Modify message → Change route |
| Route | Zoho host added in 4.1 |
| Account types to affect | Unrecognized / Catch-all only |
| Organisational unit | Top-level (applies domain-wide) |
05Dependencies & Preconditions
- SPF and DKIM must be correctly published for the domain — routed mail is only recognised as authenticated internal traffic if the domain passes these checks.
- Zoho must be configured to accept relayed mail for this domain from Google's sending IP ranges (confirm with Zoho support / allowlist as needed).
- A destination mailbox or distribution address must exist on the Zoho side to receive the catch-all traffic.
- Gmail Settings admin privilege is required to edit Hosts and Routing.
06Risks & Considerations
07Test Plan
| Test case | Expected result | Status |
|---|---|---|
| Send to existing user address | Delivered to Gmail inbox, unaffected | Pass |
Send to random non-existent address (e.g. asdf1234@domain.com) | Relayed to Zoho catch-all mailbox, no bounce | Pending |
| Send to a suspended user | Not covered by this rule — verify against Default Routing behaviour | N/A |
| SPF/DKIM check on relayed message at Zoho | Passes authentication, not flagged as spam | Pending |
08Rollback
Disable or delete the Routing rule created in step 4.2. Mail to unrecognised addresses immediately reverts to bouncing at Google's SMTP boundary; no changes to existing user mailboxes are made by this design, so rollback carries no data-loss risk.