550 5.4.5: The sender reached a daily sending limit (Google)

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 5.4.5: “Mail system congestion” in the IANA registry (RFC 3463), in the group network and routing status (RFC 3463 §3.5).
• Who uses it: Google (Gmail and Google Workspace): daily user sending limit or SMTP relay limit exceeded.

Google refused to send your message because your account, or your organization's SMTP relay, has hit its daily sending limit. The recipients are fine; the block is on your side and lifts with time.

What it means

In the IANA registry, X.4.5 is "mail system congestion", which RFC 3463 §3.5 treats as transient only. Google uses 550 5.4.5 for something more specific: a sending quota was used up. It returns the code in two documented cases (Google's SMTP error reference):

• The daily sending limit for a user account was exceeded.
• The daily limit of a Google Workspace domain's SMTP relay service was exceeded.

The bounce comes from Google's own servers when you try to send, not from the recipient's provider. The 550 means this message will not be sent; you have to send it again later.

Common causes

• A newsletter or mass mailing sent from a normal Gmail or Workspace mailbox.
• An application or device that sends through the account and was misconfigured or stuck in a loop.
• A mail merge or CRM integration sending one message per contact from the user's mailbox.
• A compromised account used to send spam.
• In Workspace, many devices and apps sharing one domain's SMTP relay quota.

Related limits at other providers

Microsoft 365 has its own sending limits with different codes: 552 5.2.2 when an account exceeds its submission quota, and 5.1.90 when it reaches its daily recipient limit (Exchange Online NDR reference).

How to fix it

1. Stop the sending that caused it. Pause the campaign, script or integration before you do anything else.
2. Check the account's Sent folder for messages you did not send. If you find any, change the password and review recent sign-ins first.
3. Wait for the daily limit to reset, then send the remaining messages in smaller numbers.
4. In Google Workspace, find which apps and devices send through the SMTP relay, and spread or reduce that traffic.
5. For regular bulk mail, use a service built for bulk sending rather than a user mailbox. Bulk mail to Gmail accounts also has to meet Google's sender guidelines, including SPF, DKIM and DMARC, and one-click unsubscribe for marketing and subscribed messages.
6. If you are sending to many recipients in one message, see also 452 4.5.3 for per-message recipient limits.

Related codes

• 552 5.2.2: The mailbox is full (or, in Microsoft 365, the sender is over quota)
• 421 4.7.28: Unusual sending rate or unsolicited mail: rate limited
• 452 4.5.3: Too many recipients in one message

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.