552 5.2.2: Mailbox full
552 5.2.2 is a permanent "mailbox full" or storage-limit failure. On Gmail it describes the recipient's inbox. On Microsoft 365 it can describe your own sending limit instead, so read the text.
- Bounce type
- Hard bounce (permanent)
- Usually caused on
- Either side, read the text
- Terlido report label
- Mailbox full
What the standard says
RFC 5321 defines 552 as "exceeded storage allocation": the mailbox has no space left for the message. RFC 3463 defines 5.2.2 as "Mailbox full": the mailbox is full because the user went over a storage quota. Class 5 marks it as a permanent failure, as opposed to the temporary 4.2.2 version.
What the mailbox providers say
- Gmail (552 5.2.2): “The recipient's inbox is out of storage space and inactive...” Source
- Microsoft 365 / Outlook (5.2.2): “Submission quota exceeded” Source
Common causes
- An abandoned mailbox that filled up over time. This is the usual meaning when Gmail adds the word inactive.
- A recipient who never clears their inbox and has hit the storage limit.
- On Microsoft 365, the sender went over the Exchange Online limit for recipients or messages in a period. Here the full side is yours, not the recipient's.
- Too many sends from one mailbox in a short time, which hits the sending quota of that mailbox.
- A trial or free account whose storage limit is small and which the owner stopped checking long ago.
- On Microsoft 365, a burst of campaign mail from one mailbox, when the daily plan for that mailbox was set too high.
How to fix it
- For a recipient with a full or inactive inbox, remove the contact. An unused inbox will not read your email anyway.
- If the text says Submission quota exceeded, lower your volume from that Microsoft 365 mailbox and wait for the limit window to pass.
- Spread sending across more mailboxes and domains, and keep each one inside its daily limit.
- Use a volume calculator to plan a send level that fits your mailbox limits before you launch.
- Count the messages each mailbox sends per day, including warmup mail, and keep the total below what the provider allows.
- Do not retry a permanent full-mailbox failure. Remove the contact and move on.
Is it a deliverability problem?
A permanent full inbox is not your fault, but the Microsoft meaning is. Hitting your own sending quota tells you that you push more mail through a mailbox than it is meant to carry. Reduce the daily volume per mailbox, add mailboxes, and let warmup raise the volume slowly. Read the provider name first. For Gmail the code is about the other person and has little to do with your reputation. For Microsoft it can point at your own habits. In both cases, repeated permanent failures push your bounce rate up, so removing the address quickly matters.
How Terlido handles it
When a bounce message for this code arrives in a connected mailbox, Terlido reads the status code. An enhanced code that starts with 5 is a hard bounce. In the campaign Reports tab this one is grouped as "Mailbox full".
On a hard bounce Terlido adds the address to the workspace blocklist with the reason "hard bounce", so no campaign emails it again. The lead stops in that campaign as bounced, its lead score goes down by 15, and the bounce counts toward the campaign's bounce rate.
Once a campaign has at least 20 sends, it pauses itself when hard bounces divided by sends goes over the campaign's maximum bounce rate. The default is 5%. If the cause was on your side and you fixed it, you can remove the entry on the Blocklist page of your account settings and try again.
Check the domain behind the bounce
The free domain checker runs live SPF, DKIM, DMARC, MX and blocklist lookups and explains each result in plain English.
Free tools that help
- Cold email sending volume calculatorEstimate first touches and total email capacity while reserving room for warmup and follow-ups.
- Mailbox and domain calculatorEstimate mailboxes and domains needed for a weekly first-touch target.
Related error codes
- 452 4.2.2: Mailbox full (temporary)
- 550 5.2.1: Mailbox disabled or not accepting mail
- 550 5.1.1: Recipient address does not exist