What 550 5.4.5 Means
The sending mailbox has hit Google's outbound daily quota. Per Google's published limits, paid Workspace users can send 2,000 outbound messages/day; free consumer Gmail caps at 500/day. The quota is rolling over a 24-hour window, not calendar day.
Google Workspace users and consumer Gmail users sending outbound. The error appears in the bounce-back to the sender, not as a rejection to the recipient.
Sending mailbox exceeded its outbound limit. Common in cold email when a single mailbox is pushed too hard — some sending platforms default to 30-50/day/mailbox but accidentally configurations can ramp up to hundreds per mailbox and trip the cap.
How to Fix 550 5.4.5
- 1
Wait 24 hours — quota is rolling
Google's quota is rolling 24h from the most recent send, not calendar-day reset. Cut send volume from the affected mailbox immediately and wait at least 24h. The quota gradually releases as old sends age out of the window.
- 2
Reduce per-mailbox daily send rate
If you're hitting 5.4.5, you're sending too much per mailbox. Cold email's deliverability-safe per-mailbox volume is 2-5 outbound/day, not the 30-50 some platforms allow. Reconfigure your sending platform to cap each mailbox at a safe number.
Note: ColdRelay's recommended cap is 2 outbound + 2 warmup per mailbox/day. This is well below Google's quota AND optimized for deliverability.
- 3
Add more mailboxes — don't push existing ones harder
Scaling cold email volume is structurally about adding more mailboxes, not increasing per-mailbox volume. 100 mailboxes at 2/day = 200/day total, safely under any quota. 5 mailboxes at 40/day = same total but burns each mailbox's reputation. Use the Mailbox Calculator at coldrelay.com/tools/mailbox-calculator.
- 4
If high-volume cold email — move off Google
Google Workspace's 2,000/day cap and reputation monitoring make it a poor fit for high-volume cold email. Most cold email senders at scale use dedicated infrastructure designed for the workload. ColdRelay's per-mailbox model on Microsoft 365 + isolated Azure tenants doesn't have a daily-quota-trip pattern — the volume is naturally bounded by the per-mailbox cap.
References
550 5.4.5 in the Cold Email Context
5.4.5 is a hard signal you've over-loaded a mailbox. The structural problem with hitting this cap regularly: Google interprets sustained near-cap sending as bulk-mail behavior and degrades the mailbox's reputation alongside the quota response. Pushing mailboxes to their daily quota burns through their reputation fast. ColdRelay's 2/day/mailbox cap exists specifically because the cost of pushing harder (reputation damage, deliverability degradation) far exceeds the cost of just adding more mailboxes. With per-mailbox pricing at $0.55-$1.00, adding 50 mailboxes is cheaper than burning out 10.
Frequently Asked Questions
What's the exact daily quota?
Per Google: 2,000 messages/day for paid Workspace users; 500/day for consumer Gmail; 10,000/day for Workspace SMTP relay (per user). Trial Workspace and Workspace Individual have lower limits.
Does receiving mail count against the quota?
No. The quota is purely outbound. Inbound mail to the mailbox is unrestricted.
Can I get my quota increased?
Generally no for cold email use cases. Google's quotas are designed to prevent abuse and they don't expand for marketing/sales outreach. Some Workspace customers can negotiate quota increases for legitimate transactional volume, but cold email isn't typically eligible.
Is 5.4.5 a hard or soft failure?
Permanent for the current 24-hour window. The message won't deliver during the cap period. Most sending platforms re-queue the message for after the quota release, treating it as a transient defer at the platform level even though the SMTP code is 5xx.