550 5.2.1 means the mailbox exists but cannot receive mail. Most of the time it has been disabled: the provider or the company switched the account off. In that case the address is as good as gone, and you should remove it.

There is one important exception from Gmail, covered below, where the mailbox is perfectly fine. Read the text after the code before you decide. For other codes, see our guide to SMTP bounce codes.

What the error looks like

Provider Message What it means
Gmail 550 5.2.1 The email account that you tried to reach is disabled. The account is switched off. Remove the address.
Gmail 550 5.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered. The mailbox works but is getting too much mail right now. Try again later.
Other servers 550 5.2.1 Mailbox disabled, account inactive, account suspended The account is switched off. Remove the address.

What the code means

  • 550: the server will not accept the message.
  • 5.2.1: "mailbox disabled, not accepting messages". The 2 means the problem is the mailbox, not the address (that would be 5.1.x) or your setup (5.7.x).

Why mailboxes get disabled

  • The person left the company and IT disabled the account instead of deleting it.
  • The account was unused for a long time, and the provider deactivated it.
  • The provider suspended it, for example for abuse or a policy violation.

Disabled accounts very rarely come back, and when they do, it is usually for a different person. Long-unused addresses are also a source of spam traps later. See spam traps.

What to do

  1. Disabled, inactive or suspended: remove the address and add it to your suppression list, like a hard bounce. Do not retry.
  2. "Receiving mail at a rate…" (Gmail): keep the address. This is a rate limit on the recipient's side, often because of a mailing list or an automated system sending them a lot of mail. Your server retries; if it keeps failing, send again later. If it happens with many Gmail recipients at once, slow your own sending down.
  3. If a contact matters, find their new address another way (LinkedIn, the company's website, a colleague).

How email verification handles it

When MailQuell checks an address and the server answers that the mailbox is disabled, the result is disabled with the advice do not send: the account exists but nobody will receive your message. When Gmail answers "receiving mail too quickly", the mailbox is not judged at all: the result stays unknown (and, like every unknown result, costs no credit), so you can check it again later.

You can check a single address with the free email checker, or upload a list to find disabled mailboxes before they bounce.

Frequently asked questions

Is 550 5.2.1 a hard or soft bounce?

Usually hard: a disabled mailbox does not come back, so treat it like an address that does not exist. Gmail's "receiving mail at a rate" message is the exception: it is temporary.

What is the difference between 5.2.1 and 5.1.1?

5.1.1 means the address does not exist at all. 5.2.1 means it exists (or existed) but the mailbox is switched off. In practice you remove both from your list.

Can a disabled Gmail account be reactivated?

Sometimes the owner can recover it for a while after it is disabled, but you cannot know whether they will. Do not keep sending in the hope that it comes back.

Sources