What 550 5.7.1 Means
If you use Google Workspace's SMTP relay service (smtp-relay.gmail.com) to send mail through Google's infrastructure, you're capped at Google's published per-user daily limit (10,000 messages/day for paid Workspace; lower for trial). When you exceed it, Google returns 550 5.7.1 with text 'Daily SMTP relay limit exceeded'.
Google Workspace SMTP relay endpoint (smtp-relay.gmail.com:587). Not seen when sending via your own SMTP server.
You sent more than 10,000 messages through Google's SMTP relay in a 24-hour window. This is a hard per-user cap; relaying multiple users' mail through one Workspace user account accumulates against that user's limit, not a domain-wide pool.
How to Fix 550 5.7.1
- 1
Verify you're using the SMTP relay endpoint
smtp-relay.gmail.com is Google Workspace's outbound relay. If your sending platform is configured to point at this host, you're subject to the 10,000/day per-user cap. Most cold email sending uses individual mailbox SMTP (smtp.gmail.com) which has different limits (2,000/day per user for paid Workspace).
- 2
Wait 24 hours for the limit to reset
Google's relay limit is rolling 24-hour. Once you cross the threshold, you wait — there's no bypass. After 24h with reduced volume, the relay accepts again.
- 3
If sending high volume — move off SMTP relay
Google's SMTP relay isn't designed for high-volume cold email. The per-user 10,000/day cap and Google's anti-abuse monitoring make it a poor fit. Cold email at scale runs on dedicated infrastructure, not Google Workspace relay. ColdRelay provides dedicated Microsoft 365 mailboxes on isolated Azure tenants — purpose-built for cold email volume.
- 4
If staying on Workspace — spread across users
If you have to use Workspace SMTP, distribute relay traffic across multiple Workspace users. With 5 users, you get 50,000/day relay capacity. Each user's traffic must be authenticated as that user — no shared credentials.
- 5
Consider whether Workspace fits your cold email model
Google Workspace's economics for cold email are poor: $6+/user/month, anti-abuse monitoring that flags cold email patterns, and tight rate caps. Most cold email senders find dedicated cold-email infrastructure (ColdRelay $0.55-$1.00/mailbox/month) more cost-effective and operationally cleaner.
References
550 5.7.1 in the Cold Email Context
Google Workspace's SMTP relay is one of the most common starter setups for cold email — until volume forces a move off. The 10,000/day cap is fine for small senders but becomes the binding constraint as you scale. The economics also work against Workspace at cold-email scale: $6+/user/month for 100 mailboxes is $600+/month before the sending platform's cost. ColdRelay's per-mailbox pricing ($0.55-$1.00) at 100 mailboxes is $55-$100/month — an order of magnitude cheaper, on infrastructure purpose-built for cold email (dedicated IPs, isolated tenants, no Google anti-abuse interference).
Frequently Asked Questions
Can I increase the SMTP relay limit?
Not really. Google's limits are firm. You can spread across more users, but the per-user cap is fixed at 10,000/day for paid Workspace. Cold email at scale outgrows Workspace within months.
What's the difference between SMTP relay and Gmail SMTP?
SMTP relay (smtp-relay.gmail.com) authenticates by domain and IP; Gmail SMTP (smtp.gmail.com) authenticates by user. Relay supports bulk routing through Google for mail with custom From addresses. Each has different limits and use cases.
Does the limit affect inbound mail?
No. SMTP relay limits apply only to outbound mail sent via Google's relay endpoint. Inbound mail to Workspace users isn't subject to the same limit.
Will Google increase my limit if I'm a good sender?
Generally no. The 10,000/user/day cap is structural, not reputation-based. Even excellent senders can't exceed it. The way to scale is to add users or move to non-Google infrastructure.