452 4.2.2: The mailbox is full
At a glance
- Type: temporary failure (class 4, RFC 3463 §2). The sending server keeps the message and retries later (RFC 5321 §4.5.4.1); it bounces only if the problem lasts until the message expires.
- Basic code 452: “Requested action not taken: insufficient system storage” (RFC 5321 §4.2.3).
- Enhanced code 4.2.2: “Mailbox full” in the IANA registry (RFC 3463), in the group mailbox status (RFC 3463 §3.3).
The recipient's mailbox is full right now. This is a temporary failure: your server keeps the message and tries again, and it is delivered if the owner frees up space in time.
What it means
RFC 3463 §3.3 defines X.2.2 as "mailbox full": the user has passed a per-mailbox quota or the physical capacity. The RFC points out that the recipient can delete messages to make room, and says the code should be used as a persistent transient failure. That is exactly the 4.2.2 form. The basic code 452 means the action was not taken because of insufficient storage (RFC 5321 §4.2.3), and like every 4yz reply it invites a retry (RFC 5321 §4.2.1).
Note the difference from X.3.1, "mail system full", which is about the whole server's storage. A 4.2.2 is about one mailbox.
Common causes
- The person has not cleaned up their mailbox in a long time and reached their storage limit.
- Large attachments, such as photos or reports, filled the quota quickly.
- The mailbox is no longer read, so nobody deletes anything and it stays full.
How providers use it
Gmail returns 452 4.2.2 when the recipient's inbox is out of storage space; its text points the recipient to managing their storage (Google's SMTP error reference). When the mailbox is both full and inactive, Gmail returns the permanent 552 5.2.2 instead.
How to fix it
- Let your mail server retry. RFC 5321 §4.5.4.1 says retries should generally be at least 30 minutes apart and continue for at least 4 to 5 days before the sender gives up.
- If the message is important and you know the person, tell them through another channel that their mailbox is full.
- Keep attachments small, or share large files as links, so a nearly full mailbox can still take your message.
- If you send through an email platform, check how it records these deferrals and after how many it stops sending to an address.
What to do with the address
Keep it for now. One mailbox-full bounce is not a reason to remove a contact. If the same address keeps coming back as full across several sends spread over weeks, the mailbox is probably no longer read. At that point treat it like a hard bounce and suppress it, or move it to a re-confirmation step.
Related codes
- 552 5.2.2: The mailbox is full (or, in Microsoft 365, the sender is over quota)
- 550 5.2.1: The mailbox is disabled and takes no mail
- 450 4.2.1: The recipient is receiving mail too fast: try later
See every bounce code in the dictionary.
Many bounces from addresses that do not exist can be avoided: check an address with our free email checker, or clean a whole list before you send.
How we wrote this: drafted by the email-validation.org team with the help of AI writing tools, from our product documentation and the sources linked in the text.