What 550 5.4.6 Means
Gmail's mail handler detected the message has been routed in a loop. Per RFC 3463, 5.4.6 is 'routing loop detected.' The most common Gmail scenario: a recipient has set up auto-forwarding from one mailbox to another, but the destination is configured (incorrectly) to forward back to the source. The message bounces between them until Gmail kills the loop.
Gmail consumer accounts and Google Workspace domains. Other receivers issue similar enhanced codes (5.4.x is the 'mail routing' category).
Recipient has misconfigured forwarders; user has an aggressive auto-reply that triggers a forwarder which triggers the auto-reply; or DNS or MX records are misconfigured such that mail to one address resolves back to a server that sends it onward to the same address.
How to Fix 550 5.4.6
- 1
Confirm 5.4.6 isn't on your side
If your sending platform's mailboxes are forwarding to themselves (rare misconfiguration), the loop is on your side. Verify your outbound mailboxes don't have any auto-forwarding configured.
- 2
If the loop is at the recipient — you can't fix it
Most 5.4.6 events are recipient-side. You're sending to an address whose user has set up bad forwarding rules. There's no way for you, the sender, to fix the recipient's mailbox configuration.
- 3
Wait — the user may notice and fix it
If the recipient is a real user and the loop is recent (e.g. just-misconfigured auto-forward), they'll likely notice and fix it. Retry the send after a few days.
- 4
If persistent — the address is functionally dead
If 5.4.6 persists for the same recipient over weeks, the loop is structural in their setup. The address is effectively undeliverable. Mark invalid and move on.
- 5
Don't keep retrying — it's wasted send budget
Sending into a confirmed routing loop wastes your IP's send budget and accumulates rejection statistics on your IP. Move on to other prospects.
References
550 5.4.6 in the Cold Email Context
Routing loops are noise in cold email — they're recipient-side configuration problems you can't fix. The cold-email-specific takeaway: a recipient with a routing loop is also likely a recipient who isn't actively using their inbox (they wouldn't have noticed the loop), so they're a low-quality prospect regardless. ColdRelay's bounce classification tracks 5.4.6 events so you can deprioritize addresses that consistently fail with routing-loop status.
Frequently Asked Questions
Is 5.4.6 my fault or the recipient's?
Almost always the recipient's. Their forwarding setup is broken. You're the messenger; there's nothing you can do from the sending side.
Can I send around the loop?
Only if you have an alternate address for the prospect. The address that triggers the loop is undeliverable; find another route to the prospect via LinkedIn or company directory.
Will the loop self-resolve?
Sometimes. If the user notices and fixes their forwarding, yes. Many users never notice because they're not actively using the affected inbox — those addresses stay broken indefinitely.
Does 5.4.6 affect my reputation?
Marginally. Receivers track non-delivery rates; persistent 5.4.6 to the same address signals you're not maintaining your list. The reputation impact is small but real — remove confirmed-loop addresses from your list.