SMTP 550 5.7.28
unusual rate of unsolicited mail (Gmail)
SMTP 550 5.7.28 means Gmail is blocking mail from your IP because it has seen an unusual rate of unsolicited email from it. Google's message reads "There is an unusual rate of unsolicited email originating from your IP address." It is the hard version of the 421 4.7.28 deferral.
Should you remove the address?
Keep the address; fix the sending side
Keep the addresses, but don't send to any of them from that IP until the block lifts. The cause is your sending pattern.
Block. Retrying changes nothing until the cause on your side is fixed.
How it appears
550 5.7.28 There is an unusual rate of unsolicited email originating from your IP address. To protect our users from spam, mail sent from your IP address has been blocked.
What causes it
- A burst of cold or bulk email from an IP with little history.
- High spam complaint rates or spam-trap hits.
- A compromised server or account sending spam from your IP.
How to fix it
In order — try the first one first.
- Stop sending to Gmail from that IP until you have found the cause.
- Check Google Postmaster Tools for spam rate and IP reputation.
- Only send to people who expect your mail, and clean the list before resuming.
- Resume at low volume and increase it gradually.
Who sends it
Gmail and Google Workspace.
Gmail
Reply text There is an unusual rate of unsolicited email originating from your IP address. To protect our users from spam, email sent from your IP address has been blocked.
Gmail points to its bulk sender guidelines.
Common questions
- What does SMTP 550 5.7.28 mean?
- SMTP 550 5.7.28 means Gmail is blocking mail from your IP because it has seen an unusual rate of unsolicited email from it. Google's message reads "There is an unusual rate of unsolicited email originating from your IP address." It is the hard version of the 421 4.7.28 deferral.
- Should I retry a 550 5.7.28 error?
- No. 550 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 550 5.7.28?
- Stop sending to Gmail from that IP until you have found the cause.
- Is 550 5.7.28 a hard bounce or a soft bounce?
- 550 5.7.28 is a block rather than a classic hard or soft bounce. The rejection is about your sending (authentication, reputation, content or the recipient's policy), not about whether the address exists. Retrying changes nothing until the cause on your side is fixed.
- Should I remove the address after a 550 5.7.28 bounce?
- Keep the addresses, but don't send to any of them from that IP until the block lifts. The cause is your sending pattern.
- Will verifying my list prevent 550 5.7.28?
- Not directly. This code is about your authentication, IP or domain reputation, so verification will not lift it. A clean list still matters, because mailbox providers weigh how often a sender hits addresses that don't exist.
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.
Other 550 replies
- 550 5.1.1 — mailbox does not exist
- 550 5.7.1 — message refused by policy
- 550 5.4.1 — recipient address rejected, access denied
- 550 5.2.1 — mailbox disabled, not accepting messages
- 550 — mailbox unavailable
- 550 5.1.0 — address rejected, other address status
- 550 5.1.10 — recipient not found (Microsoft 365)
- 550 5.1.8 — bad outbound sender (Microsoft 365)
- 550 5.4.5 — daily sending limit exceeded (Gmail)
- 550 4.4.7 — message expired in the queue
- 550 5.7.25 — no PTR record for sending IP (Gmail)
- 550 5.7.26 — blocked, sender unauthenticated (Gmail)
- 550 5.7.27 — SPF authentication failed (Gmail)
- 550 5.7.23 — SPF violation (Microsoft 365)
- 550 5.7.124 — sender not in allowed senders list (Microsoft 365)
- 550 5.7.509 — DMARC failed, policy reject (Microsoft 365)
- 550 5.7.606-649 — banned sending IP (Microsoft)
- 550 5.7.705 — tenant has exceeded threshold (Microsoft 365)
- 550 5.7.708 — traffic not accepted from this IP (Microsoft 365)
- 550 5.7.750 — blocked from sending from unregistered domains (Microsoft 365)
- 550 5.7.515 — authentication required for high-volume senders (Outlook.com)
- 550 5.7.1 S3140 — IP range on Outlook.com block list
- 550 5.5.0 — Mailbox unavailable (Outlook.com, Hotmail)
- 550 5.7.12 — Sender not authenticated by organization (Microsoft 365)
- 550 5.7.513 — Blocked by the recipient's own block list (Microsoft 365)
Sources
- Source: Google Workspace Admin Help: Gmail SMTP errors and codes
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22