Are 446, 447, and 449 real SMTP error codes?

The complete set of base SMTP reply codes RFC 5321 defines in the 4yz temporary-failure class

is 421, 450, 451, 452, and 454 (plus a handful of extension-specific codes like 455 for

unmet size parameters). 446, 447, and 449 are not among them. No compliant SMTP server

generates these as literal reply codes. As with other invented-looking numbers in this range, they

most likely originate from a monitoring or bounce-management tool's internal classification scheme

rather than anything that appeared on the wire.

The codes, mapped to what is real

The 446 case is worth noting specifically: "queued mail for delivery" is not an error condition

at all under the real protocol — a message being queued is a success reply (250), not a

failure. If a tool reports "error 446" for a message still in transit, it most likely means the

message has not yet reached a final state, not that anything has actually failed.

SMTP Email Error 446 (as commonly mislabelled)

DATA
354 Start mail input
...
.
250 2.0.0 Queued as 4R2x1S0ab2z

A successfully queued message gets a 250, not an error code. If a sending platform's dashboard

shows "446" for a message in this state, treat it as "still processing," not as a failure to

investigate.

SMTP Email Error 447 (Timeout Exceeded), the real version

RCPT TO:<recipient@example.com>
451 4.4.7 Delivery time expired, retrying

This is a genuine, standard condition: your own sending queue (or an intermediate relay) has been

unable to complete delivery within its configured retry window and is reporting that the attempt

has timed out. It becomes a locally generated non-delivery report once your own MTA gives up

entirely, which is why the final bounce you see may not carry a code from the recipient's server

at all.

SMTP Email Error 449 (Routing Error), the real version

RCPT TO:<recipient@example.com>
551 5.4.4 Unable to route, message refused

551 and 554 5.4.4/451 4.4.4 cover this condition depending on whether the routing failure is

treated as permanent or temporary by the server that generated it.

Step-by-step: finding the real code

1. Get the raw SMTP transcript or the raw NDR source, not a dashboard's summary classification.
2. Check whether a `250` success reply preceded the "error" — if so, the message was

successfully queued and any later "error" label is about delivery status after acceptance, not

a rejection.

1. Match the real condition (timeout vs. routing) to its actual RFC 5321/3463 code — `451

4.4.7 for timeout, 551/554 5.4.4 or 451 4.4.4` for routing, depending on severity.

1. Treat the leading digit of the real code (4 vs 5) as authoritative for whether a retry is

still in progress or the message is permanently undeliverable.

Utilizing email warm-up services in this context

None of these three conditions — queuing, delivery timeout, or routing failure — are caused by

sender reputation, and warming up a mailbox does not directly prevent them. Where warm-up does

help is in reducing the likelihood that a message sits in a provider's deferred queue long enough

to approach a real timeout, since clean, established sending reputation is processed with fewer

precautionary delays at most receivers.

What not to do

• Do not search RFC 5321 for "446", "447", or "449" expecting a definition — none exists, and the

time is better spent reading the raw transcript.

• Do not treat "446: queued for delivery" as an error requiring action — it most likely represents

a successful 250 queue acceptance, and chasing it as a failure wastes time on a message that

may well still deliver normally.

• Do not build bounce-handling logic keyed on these three numbers directly — key it on the real

RFC 5321/3463 codes behind each condition, since a tool's internal numbering can change without

notice.

MailPilot surfaces the actual SMTP reply and enhanced status code behind every delivery event

rather than a paraphrased internal category, which is the reliable way to tell a genuine `451

4.4.7` timeout apart from a tool's shorthand for one, or from a message that was never actually in

trouble at all.