550 5.2.1: The mailbox is disabled and takes no mail
At a glance
- Type: permanent failure (class 5, RFC 3463 §2). The sending server does not retry; sending the same message again fails the same way until the cause is fixed.
- Basic code 550: “Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)” (RFC 5321 §4.2.3).
- Enhanced code 5.2.1: “Mailbox disabled, not accepting messages” in the IANA registry (RFC 3463), in the group mailbox status (RFC 3463 §3.3).
The mailbox exists, but it is switched off and refuses mail. Most often the account is inactive or suspended; at Gmail it can also mean the mailbox received mail so fast that delivery was blocked.
What it means
RFC 3463 §3.3 defines X.2.1 as "mailbox disabled, not accepting messages": the mailbox exists but does not take messages. The RFC notes this can be permanent if the mailbox will never be enabled again, or transient if it is only disabled for a while. With a 550 basic code and a 5.2.1 enhanced code, the server is telling you it is a permanent refusal (RFC 5321 §4.2.1). Its temporary counterpart is 450 4.2.1.
The difference from 550 5.1.1 matters: 5.1.1 says there is no such mailbox; 5.2.1 says there is one, but it is not in use.
Common causes
- The account was abandoned and the provider marked it inactive.
- The account was suspended, for example for a policy violation or an unpaid service.
- An employer disabled the mailbox of someone who left but has not deleted it yet.
- At Gmail: a sender kept mailing one recipient at a rate that turned temporary deferrals into a block.
How providers use it
Gmail returns 550 5.2.1 for two documented reasons: the recipient's account is inactive, or the user is receiving mail at a rate that prevents further delivery (Google's SMTP error reference). The bounce text says which one applies, so read it before deciding what to do.
How to fix it
If the text says the account is inactive or disabled:
- There is nothing to fix on your side. Only the owner or their provider can reactivate the account.
- If the contact matters, reach them another way and ask for a current address.
If the text is about the receiving rate:
- Stop sending to that recipient for a while and find the source of the volume: an alert loop, repeated notifications or a stuck retry.
- Add a limit on how many messages one recipient can get from your system in a given time.
- Send again later at a normal pace.
What to do with the address
For an inactive or disabled account, suppress the address like any hard bounce. An inactive mailbox is not read, so mail to it reaches nobody. For a rate block, keep the address but fix the sending pattern first. If inactive-account bounces are common in your list, older contacts are going stale; the list cleaning guide covers how to deal with that.
Related codes
- 550 5.1.1: The recipient mailbox does not exist
- 552 5.2.2: The mailbox is full (or, in Microsoft 365, the sender is over quota)
- 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.