Bounce and error codes

550 5.2.1 The email account that you tried to reach is inactive

Last updated 2026-09-03

The receiving server found the mailbox you wrote to, and then it refused the message. The bounce reads 550 5.2.1. RFC 3463 assigns those digits to a mailbox that exists and is not accepting messages. Your DNS records did not cause this, and editing them will not clear it. Someone who runs mail for that address owns the fix. The last section of this page is the message to send that admin.

Gmail prints inactive; live NDRs still print disabled

Google's Gmail SMTP error table lists two rows under 550 5.2.1. The first is the inactive-account sentence.

Live bounces quoted on Google's own help community still print disabled in place of inactive, with the same help URL. I copied this form from those threads, with the NDR still attached.

A log that wraps the reply across two SMTP lines puts a hyphen on the first line. RFC 5321 defines that form. A hyphen after the code means more text follows. A space means the reply ends there.

The help parameter is DisabledUser on every variant. When I opened that URL, Google served the generic Fix bounced or rejected emails article. It does not document the inactive account itself. The SMTP table is the page that names the cause.

Outlook wraps a Microsoft-side bounce under Your message couldn't be delivered. A Gmail bounce arrives from Mail Delivery Subsystem.

Gmail reuses 5.2.1 for a receive-rate refusal

The second 550 5.2.1 row in Google's table is a different refusal. It names the rate at which that mailbox is receiving mail, not the account's enabled state.

The temporary twin uses the same sentence with 450 4.2.1, and it tells you to resend later. The 550 form is permanent for the message you just sent. Neither string is a disabled mailbox. Slow down, or wait, rather than writing to their admin about a suspension that nobody ordered.

RFC 3463 gives 5.2.1 to a mailbox that exists

RFC 3463 section 3.3 prints the definition in two sentences: "The mailbox exists, but is not accepting messages. This may be a permanent error if the mailbox will never be re-enabled or a transient error if the mailbox is only temporarily disabled." The leading 5 or 4 is what tells your server which of those two the receiver chose.

The same section says mailbox issues "are assumed to be under the general control of the recipient." The person who can re-enable the mailbox sits inside the receiving organisation. You cannot do that from outside.

550 5.1.1 is the neighbouring code for a mailbox the server never found. 5.2.1 means it found one and then refused it. The two bounces feel the same from your inbox. The directory work on their side is not the same.

Exchange Online's public table has no 5.2.1 row

Microsoft's Exchange Online NDR table has no row for 5.2.1. Do not treat a Microsoft 365 bounce as 5.2.1 from the digits alone if the words say something else. If the bounce is 5.2.121 or 5.2.122, you are still on the right page for the prefix. Those two rows are documented.

• 5.2.121 Recipient's per hour message receive limit from specific sender exceeded. One sender hit the hourly cap to that one mailbox.
• 5.2.122 Recipient's per hour message receive limit exceeded. The mailbox hit its hourly cap from all senders.

Both are receive-rate throttles, not a disabled mailbox. Microsoft's Mailboxes exceeding receiving limits report is the admin view for diagnosing them. Slow down and retry later. Do not write to their admin about a suspension.

On-premises Exchange documents a different 5.2.1. Microsoft's Exchange Server NDR page lists 5.2.1 as Content Filter agent quarantined this message. That bounce is a spam quarantine. The mailbox is still enabled. Email quarantined covers that family. If your bounce names the Content Filter agent, work that page.

Live Exchange NDRs, mostly from on-premises threads, have quoted a store-driver line with 5.2.1 as the enhanced status code. The leading SMTP code on this live string is 554, not 550. The enhanced status code is still 5.2.1.

Support threads quote that string with the NDR still attached. Microsoft Learn does not print it. Read the exception name if it is in your bounce: AccountDisabledException and MapiExceptionMailboxDisabled are the words that name a disabled mailbox.

Removing a Microsoft 365 license does disable the mailbox. Microsoft's license-removal article says Exchange Online "immediately disconnects (disables) the mailbox if the Exchange Online license for the user is removed or expires." That article never prints 5.2.1. Microsoft Q&A staff have pointed senders at 550 5.4.1 Recipient address rejected: Access denied instead. I cannot verify a single current Exchange Online bounce string for a delicensed mailbox, so I will not invent one.

What a sender can confirm, then stop

Copy the words after 5.2.1 before you close the bounce. inactive and disabled are mailbox state. Receiving-at-a-rate is a limit. Content Filter is a quarantine. 5.2.121 or 5.2.122 is an Exchange Online hourly receive cap.

Compare the address in the bounce against the one you meant, letter by letter, the part after the @ included. Delete that person from Outlook Auto-Complete and type the address by hand. A retyped address that bounces the same way is not a cache problem.

Then use another channel. Phone the person, or ask a colleague. Mail is the one route that no longer reaches them. Ask whether the account was suspended, whether they still work there, and what address to use now.

One Microsoft 365 or Google Workspace domain bouncing, with every other domain going through, points at that mailbox. Every address at the domain bouncing the same way points at a domain-wide disable, a license batch, or a suspended tenant. After that, stop resending. 550 permanent failure covers what that leading 5 commits your own server to.

Receiving admins: re-enable the mailbox

A sender cannot switch a disabled mailbox back on. If you administer the domain in the bounce, the mailbox state is yours to reverse: restore the account, put the license back, or reconnect the store. Every sender writing to that address reads the same refusal, and the report goes to them instead of you.

• Google Workspace: you suspended the user. In the Admin console, open Directory > Users and find the account. An admin-initiated suspension blocks new mail, and Gmail answers 5.2.1. Restore the user if that suspension was a mistake. If the person left, give senders a live address rather than leaving the bounce in place.
• Google Workspace: Google suspended the account. Google's suspend-a-user page says a Google-initiated suspension (Terms of Service, a compromised account, or similar) might still deliver mail, depending on context. That case does not reliably produce a clean 5.2.1. Do not restore the user first. Follow Google's suspended-account guidance and resolve whatever triggered the suspension. Google's restore page says an admin cannot restore an account Google suspended for abuse or a Terms of Service breach.
• Microsoft 365: the license and the mailbox. Microsoft's steps for the neighbouring code 5.1.10 send an admin to Users and then Active users. Confirm the account exists and holds an Exchange Online license. Reassign the license within 30 days if it was removed, because Microsoft deletes the mailbox after that. A shared mailbox does not need a user license and still accepts mail.
• On-premises Exchange: the mailbox is disabled, or the content filter ate it. Get-Mailbox and Get-MailboxStatistics show a disconnected mailbox. Microsoft's disconnected-mailbox page is the reconnect path. If the bounce names the Content Filter agent, the mailbox is fine and the filter quarantined the message.
• Quota is a different code. RFC 3463 assigns mailbox-full to X.2.2, and it says that code should be a persistent transient failure. Gmail's table prints 552 5.2.2 The recipient's inbox is out of storage space and inactive. Secondary pages fold quota into 5.2.1. Gmail's table and Exchange Online's table put storage on 5.2.2. If your bounce names storage or quota, work 5.2.2.

Postfix has no shipped 5.2.1 sentence for a disabled mailbox. An operator who wants that code adds a check_recipient_access map and writes the reply by hand. A default Postfix unknown-user rejection is still 550 5.1.1 User unknown.

Send the receiving admin this

Nobody who can re-enable that mailbox has seen your bounce. Paste this, with the address and the exact line filled in.

Keep inactive, disabled or AccountDisabledException in the pasted line. An admin searching those tokens opens the user account. Stripping the bounce down to 550 points them at anti-spam instead.

The person who can restore that mailbox is rarely the one you wrote to. Call a colleague at the company, try a shared inbox that still answers, or ask the account manager on the contract. Forward the bounce itself; the exception name in it is what their admin will search for.

SPF, DKIM and DMARC did not cause this

The documented 5.2.1 check reads the destination mailbox. Gmail's SMTP table never mentions authentication on either 5.2.1 row. Publishing a DMARC record does not re-enable someone else's account, and tightening one does not disable it either.

Rejections that do come from your records name them in the text. 550 5.7.26 says the message is unauthenticated. 550 5.7.23 names SPF. Why an email bounces back covers reading any bounce, whichever system sent it.

550 5.2.1 against the codes it gets confused with

The digits collide with neighbouring codes. Match the sentence in the bounce, not only the 5.2.1 prefix.

Code	Text in the bounce	What it means
550 5.2.1	The email account that you tried to reach is inactive / disabled	The receiving server found the mailbox and it is not accepting mail
550 5.2.1	receiving email at a rate that prevents additional messages	Gmail's receive-rate cap, not a disabled account
5.2.121 / 5.2.122	per hour message receive limit (from specific sender / exceeded)	Exchange Online hourly receive throttle; use the Mailboxes exceeding receiving limits report
550 5.1.1	The email account that you tried to reach does not exist	The server looked the address up and found no mailbox behind it
550 5.4.1	Recipient address rejected: Access denied (often with an AS suffix)	Directory-Based Edge Blocking refused the address at Exchange Online's perimeter
552 5.2.2	The recipient's inbox is out of storage space and inactive	Gmail found the mailbox and it is over quota
5.2.1	Content Filter agent quarantined this message	On-premises Exchange quarantined the message, mailbox still enabled

Directory-Based Edge Blocking answers 5.4.1 at the perimeter when the address is not a recipient object. That is a missing address, not a disabled mailbox. 550 5.4.1 Recipient address rejected covers it. If the wording in your bounce is "Access denied" and the digits are 5.4.1, read that page instead of this one.

You fixed this sender. Tomorrow the reports name the other hosts still sending as you, and we turn a day of XML into one email with a verdict per sender. On the paid plans, the day a report first names a new sender failing, you hear about it. Get the weekly digest. The first domain is free.