550 5.4.5 — Daily user sending limit exceeded
You are being rate limited, not blocked
SMTP error 550 5.4.5 means the sending mailbox has hit its own provider-imposed daily message cap, not that the recipient rejected anything. Google Workspace allows roughly 2,000 messages per day per user via SMTP and far fewer for trial or newly created accounts. The cap resets on a rolling 24-hour window.
What the server actually says
550-5.4.5 Daily user sending limit exceeded. For more information on Gmail
sending limits go to https://support.google.com/a/answer/166852 - gsmtpWhat you see
Sends succeed normally for part of the day and then every send fails with the same error until the rolling window clears. Warmup appears to "break" at the same time each day.
Why it happens
- The mailbox genuinely reached its daily cap - the cap counts recipients, so one message to 30 people costs 30.
- The account is new or on a trial: Workspace trial accounts are capped far below the documented 2,000/day.
- Several tools are sending from the same mailbox and their volumes add up against one shared cap.
- A warmup ramp was configured above what the account tier actually permits.
How to fix it
- Find the real cap for the account tier. Workspace trial and newly provisioned accounts are limited well below 2,000/day. Treat the documented number as a ceiling, not an entitlement.
- Add up every tool sending from the mailbox. Sequencer, warmup, and transactional mail share one quota. The cap is per mailbox, not per application.
- Lower the daily target below the cap. Leave real headroom. Running at 95% of a cap means any burst pushes you over and stalls the rest of the day.
- Spread sends across more mailboxes, not more volume per mailbox. The safe path to higher volume is additional warmed mailboxes across domains, never one mailbox at its ceiling.
What not to do
- Do not stop or disable the mailbox. It is healthy - it is full. Stopping it loses the ramp progress and the reputation it has already built.
- Do not count this as a bounce. The recipient address is fine and should not be suppressed; no delivery was attempted.
- Do not immediately retry. The window is rolling and retrying inside it burns attempts without sending anything.
Frequently asked questions
How long until 550 5.4.5 clears?
It is a rolling 24-hour window, not a midnight reset. Capacity returns gradually as the oldest sends age out, so partial sending usually resumes before a full day has passed.
Does hitting the limit hurt deliverability?
The error itself does not. Repeatedly slamming into a cap is a sign of an overloaded mailbox though, and that pattern - high volume from one address - is itself a spam signal.
Is the limit per message or per recipient?
Per recipient. Google counts the number of addresses mail is delivered to, so a single message with 50 recipients consumes 50 of your daily allowance.
How MailPilot helps
MailPilot classifies this error automatically on every connected mailbox and tells you which side is at fault, so a throttle is never mistaken for a dead recipient and a credential failure never suppresses a healthy address. It also monitors real inbox placement and checks SPF, DKIM and DMARC on every mailbox, which is where most policy rejections start.
Related errors
- 451 4.7.1 — Ratelimit exceeded
- 421 4.7.0 — Too many messages - try again later
- 535 5.7.8 — Username and Password not accepted
Last reviewed 2026-10-11 by the MailPilot team.