What 550 5.4.5 means
The message Gmail attaches to this code is “Daily user sending limit exceeded.”, as written on its reference page. The first digit says how final it is: a 5xx reply is permanent for that message, so the sending server gives up and returns a bounce. The enhanced status 5.4.5 says what class of problem it is: rate limit. The sender exceeded a published cap or was throttled. Slow down and spread the volume; the cap resets.
Why it happens
The sender pushed more mail at the receiver, in a burst or across the day, than it is willing to take from a sender it does not know well. The limit is not only the published cap: a new domain sending its first hundred messages in one hour is throttled where an established one would not be.
What to do first: The Google account hit its daily cap (2,000 on Workspace, 500 on consumer Gmail). Sending resumes within 24 hours; lower the daily volume so it never gets there.
Why warming does not fix this
Warming builds sender reputation. 550 5.4.5 in this form is a rate limit problem, and no amount of engagement history changes it. Fix the cause and the bounce stops; warming is for what comes after, when the mail is accepted and the question becomes which folder it lands in. See how warming works for that part.
How to fix it, in order
- Slow the send and spread it across the day
- Check the provider's published limit
- Start outreach at 20 to 30 a day per mailbox and scale with placement, not with the cap
Related codes
- 550 5.7.1 (Gmail): rate limited
- 550 5.7.233 (Microsoft): tenant external recipient limit
- 550 5.7.236 (Microsoft): onmicrosoft.com daily limit
- 550 5.2.2 (Microsoft): submission quota exceeded
- 421 4.7.0 (Gmail): try again later
More on Gmail
- Google Workspace emails going to spam: the Postmaster-led diagnosis, dashboard by dashboard
- Gmail and Yahoo bulk sender requirements: the rules behind Google's authentication and spam-rate rejections
- Google Postmaster Tools domain reputation: what the reputation tiers and the spam rate mean
Questions about 550 5.4.5
What does 550 5.4.5 mean?
Gmail returns 550 5.4.5 with the message "Daily user sending limit exceeded.": daily sending limit exceeded. The sender exceeded a published cap or was throttled. Slow down and spread the volume; the cap resets.
Is 550 5.4.5 a hard bounce or a soft bounce?
A hard bounce for that message: the 550 reply is permanent, and the message is not retried. Whether the address should be removed depends on the cause: here the fix is on the sending side, not the list.
How do I fix 550 5.4.5?
The Google account hit its daily cap (2,000 on Workspace, 500 on consumer Gmail). Sending resumes within 24 hours; lower the daily volume so it never gets there. Gmail's own reference for the code is linked on this page.
Does email warmup fix 550 5.4.5?
No. 550 5.4.5 in this form is a rate limit problem, and warming builds reputation, which is not what is failing here. Fix the cause and the bounce stops.