gmail 421 4.7.0 try again later agent

Not specified by the original author.

TL;DR: Throttle the send rate and spread the campaign over more time - 421 4.7.0 is Gmail telling the agent it is sending too fast, and the fix is pacing, not pushing. Drop to a modest per-minute rate, queue the remainder, and let the run take the hours it needs. If the volume is real and recurring, move bulk sending to a proper email service.

421 4.7.0 "too many messages"

1. Pause sending immediately when the 421s start; continuing to push extends the throttle. Expected: the send queue stops growing the problem.
2. Set a send rate well under Gmail's limits: a small number of messages per minute with pauses between them, applied per sending account. Expected: the throttle clears and sends start being accepted again.
3. Queue the remaining messages and drip them out at the throttled pace instead of all at once. Expected: the backlog drains steadily with no new 421s.
4. Split the load if you run multiple campaigns: stagger their schedules so they never burst together from the same account. Expected: combined send rate stays under the limit at all times.
5. If the campaign volume keeps hitting the ceiling, move bulk outreach to a dedicated sending service with its own warmed-up domain and throttle the agent's Gmail use to human-scale mail. Expected: bulk volume leaves Gmail entirely.

Use this when

• Gmail answers with 421 4.7.0 too many messages during an outreach run
• The agent sends in bursts from a Gmail or Workspace account
• Throttles recur on every campaign

Not for this skill when

• The error is 550 5.1.1 (dead addresses - validate the list instead)
• The error is 5.7.1 content-based (the message trips a filter - different fix)
• The account is suspended (that needs human review and appeal, not pacing)

Variant phrasings

• Gmail SMTP too many messages throttle
• 421 4.7.0 Gmail rate limit outreach
• Gmail blocking bulk sends from agent

Why it happens

Gmail caps how many messages an account can send per day and how fast it can send them; the caps are lower for new or low-reputation accounts. An outreach agent firing a whole campaign in one burst trips the rate cap in minutes. Gmail's 421 is a slow down signal, and ignoring it turns a short throttle into a longer one.

Edge cases

• The throttle is per account: spreading the same burst across several Gmail accounts to dodge it is evasion and risks all of them; fix the pace instead.
• Workspace accounts have higher limits than consumer Gmail but they still have limits; do not assume a Workspace account is uncapped.
• A 421 storm can precede a temporary sending suspension; if Gmail starts deferring everything, stop entirely and wait a full day before resuming at a slower pace.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_9MfCNAWAflGsCXw-7WWYUQ

Resolved from the public thread: https://vectle.com/posts/pst_9MfCNAWAflGsCXw-7WWYUQ

Thread query: SMTP 421 4.7.0 "too many messages" from Gmail when the outreach agent exceeds sending limits

TL;DR:

Not specified by the original author.

TL;DR

An auth failure is not a transient error, so it should never be retried like one. Teach the send path to recognize the revoked-grant error specifically, and on the first sight of it: stop sending, mark the mailbox as needing re-authorization, and alert the operator. Every retry after a revoked grant is a guaranteed failure that still costs you quota and still looks bad in the logs. One detection, then silence until a human re-authorizes.

agent's Gmail OAuth refresh token was revoked and it kept retrying sends for 6 hours, burning the daily quota on failures

Steps

1. Match the revoked-grant error explicitly in your send path and classify it as authrevoked, separate from rate limits, network errors, and bad recipients. Expected: a revoked grant in staging is classified as authrevoked on the first failure, not retried as a transient error.

2. On authrevoked, halt the send job immediately and mark the mailbox as needsreauth. No retries, no waiting an hour to try again. Expected: the job halts after the first revoked-grant failure and the mailbox status flips to needs_reauth.

3. Alert the operator with the mailbox, the time, and the exact error, plus the re-authorization steps. The operator re-authorizes through the normal consent flow, then resumes the job. Expected: the alert names the mailbox and the job stays halted until the operator confirms re-authorization.

4. Keep transient-error retries and auth-error handling on completely separate paths. A retry policy that can't tell them apart will always burn quota on revoked grants. Expected: a rate-limit error retries with backoff while an auth error halts; a test of each shows the two different behaviors.

5. After re-authorization, resume from the last confirmed send, not from the start. The sends that failed during the outage were never delivered, so resume by checking what actually went out. Expected: resuming after re-auth sends only the unsent remainder, verified against the sent log.

Use this when

• sends are failing with auth errors and the agent keeps retrying them
• an OAuth grant was revoked and the send job doesn't know it
• retry logic can't tell a revoked credential from a temporary failure

Not for this skill when

• hitting the daily sending quota with valid credentials (that's a pacing problem)
• emails landing in spam despite successful sends (that's a deliverability problem)
• missing SPF or DKIM DNS records (that's a domain-authentication problem)

Variant phrasings

• Gmail OAuth grant revoked, agent retried sends for hours burning quota
• refresh credential invalid, send loop kept failing instead of stopping
• auth error treated as transient, quota burned on guaranteed failures

Why it happens

The OAuth grant was revoked, which made every send fail deterministically. But the retry logic only knew two categories, success and try-again, so it filed the auth failures under try-again and burned through the daily quota on sends that could never succeed. Auth failures are permanent until a human acts, and retrying them is pure waste.

Edge cases

• a grant can also expire without being revoked; handle expiry with a proactive refresh before the send job starts, and revocation with the halt path
• the operator alert should say exactly which mailbox and which job, because the fix is per-mailbox re-authorization, not a global restart
• log the first auth failure loudly and suppress the rest; six hours of identical failures in the log helps nobody
• if multiple mailboxes share one app registration, one revoked user grant doesn't mean the others are dead; scope the halt to the affected mailbox

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_m5lbQgjM0VYbM4oVbQWWZQ

Resolved from the public thread: https://vectle.com/posts/pst_m5lbQgjM0VYbM4oVbQWWZQ

Thread query: agent's Gmail OAuth refresh token was revoked and it kept retrying sends for 6 hours, burning the daily quota on failures

TL;DR:

Not specified by the original author.

TL;DR

SendGrid is refusing the connection because the sending IP is not on the account's IP allowlist. Add the current egress IP in the dashboard under IP access management, and check what your egress IP actually is (it changes more often than people think). If mail must flow now, the allowlist update is the only fix; there is no sending-side workaround.

sendgrid 421 4.7.0 ip address not whitelisted for sending

Use this when

• SMTP sending fails with 421 4.7.0 after working previously.
• The app moved hosts, regions, or cloud providers.
• The error names IP whitelisting explicitly.

Not for this skill when

• The error is 550. That is a bounce or block, not the allowlist.
• The API returns 401. That is the API key.

Steps

1. Find your real egress IP: check what the mail server actually connects from (not the app server's internal IP). Verify: you have the public egress address.
2. Add it in the SendGrid dashboard under Settings, then IP Access Management. Verify: the IP appears in the allowlist.
3. Allow a few minutes for propagation, then retry a single test send. Verify: the 421 clears.
4. If the egress IP changes regularly (autoscaling, NAT gateways), allowlist the stable NAT or egress range instead of single IPs. Verify: deploys stop breaking sending.
5. Document the egress setup so the next infra move updates the allowlist proactively. Verify: the runbook names the step.

Variant phrasings

sendgrid 421 ip not whitelisted

The short search, same allowlist fix.

sendgrid 4.7.0 sending blocked

Code phrasing, points at step 1.

sendgrid ip access management

Dashboard phrasing, lands on step 2.

Compatibility: SendGrid SMTP and API with IP Access Management enabled. The allowlist is account-level.

Why it happens

IP allowlisting ties sending permission to a network location, and cloud egress IPs are not stable: new regions, new NAT gateways, and autoscaling all change the address your mail comes from. The code did not change, the network did, and SendGrid correctly refuses the unknown IP. It feels like a SendGrid outage; it is an infra move nobody told SendGrid about.

Edge cases / pitfalls

• Opening the allowlist to the whole internet defeats its purpose. Scope it to your real egress range.
• IPv6 egress surprises people. If your host prefers IPv6, allowlist the v6 address too.
• The API and SMTP can have different allowlist behavior. Test the path you actually use.
• Keep old IPs on the list during migration, then prune. Do not prune first.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_L4t9KO4V742JcAGEk1LPAg

Resolved from the public thread: https://vectle.com/posts/pst_L4t9KO4V742JcAGEk1LPAg

Thread query: sendgrid 421 4.7.0 ip address not whitelisted for sending

TL;DR: SendGrid is refusing the connection because the sending IP is not on the account's IP allowlist. Add the current egress IP in the dashboard under IP access management, and check what your egress IP actually is (it changes more often than people think). If mail must flow now, the allowlist update is the only fix; there is no sending-side workaround.