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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Postfix has no documented universal ceiling of two emails per minute. That pattern usually means either a configured per-client limit is being enforced, a service-specific override is active, or messages were accepted and are waiting in the queue or for a remote server. Measure which stage is slow before changing a limit: check the effective configuration, correlate SMTP log events with the two-minute cadence, and inspect queue age and remote responses.
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What “two emails per minute” actually tells you
Postfix rate controls normally apply to an SMTP client’s requests, not to every message leaving the server. A client can be limited when it connects, starts TLS, authenticates, issues MAIL FROM or RCPT TO, or submits a message. Separately, a message that Postfix already accepted can remain queued because of destination-server deferrals, DNS or TLS problems, transport concurrency, or retry backoff.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsThe documented default for smtpd_client_message_rate_limit is 0, meaning unlimited. The same is true of the main per-client connection and recipient rate controls. Therefore, a repeatable two-per-minute pattern is evidence of a local nonzero setting, a service override, an application-side schedule, or a downstream delivery constraint—not a built-in Postfix maximum. See the current Postfix configuration-parameter reference.
| Where the delay occurs | Typical evidence | Correct troubleshooting branch |
|---|---|---|
| SMTP acceptance | Reject or defer responses during connection, AUTH, MAIL FROM, RCPT TO, or submission; timestamps repeat at a fixed interval |
Inspect smtpd_client_* limits, anvil counters, exceptions, and service overrides |
| Queue scheduling | SMTP client receives acceptance, but queue IDs remain for a long time before delivery attempts | Inspect queue age, transport concurrency, retry and backoff settings, and active queue processing |
| Remote delivery | Queue IDs show delivery attempts followed by temporary remote replies, DNS failures, or TLS negotiation errors | Investigate the destination host, DNS, TLS, and provider or recipient-domain deferrals |
| Application submission | The application opens a fresh connection for every small message or deliberately sleeps between sends | Batch recipients where semantics and privacy allow, and use SMTP submission rather than repeatedly invoking a local sendmail process |
Run a first diagnostic pass
Capture evidence before editing configuration. Use the same sender and test volume later so that your comparison is meaningful.
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- Record the version. Run
postconf mail_version. Rate-limit parameters and AUTH-specific controls can vary by installed Postfix version, so keep the version beside every result. - Record effective global settings. Run
postconf -n. This prints non-default settings as Postfix currently reads them, rather than only showing what you remember putting inmain.cf. - Identify the receiving service. Run
postconf -M submission/inet, replacingsubmission/inetwith the service that actually receives the traffic. A client using port 25, submission, or smtps may be reaching different services. - Print the relevant limits together. Use:
postconf smtpd_client_message_rate_limit
smtpd_client_connection_rate_limit
smtpd_client_connection_count_limit
smtpd_client_recipient_rate_limit
smtpd_client_new_tls_session_rate_limit
smtpd_client_auth_rate_limit
smtpd_client_event_limit_exceptions
anvil_rate_time_unitIf your version does not recognize smtpd_client_auth_rate_limit, omit it; that control exists only in versions that support it. Do not interpret an unknown-parameter error as proof that another limit is active.
- Search the mail log. Filter for the sender’s IP address, authenticated username, queue ID, service name, and words such as
anvil,reject, anddefer. Correlate each event’s timestamp with the apparent two-per-minute interval. The exact log location differs by operating system; use the mail facility configured for your host. - Inspect queue state. Run
postqueue -p. Note the number of queued messages, their oldest age, destination domains, and the latest status text. Select representative queue IDs and follow them through the mail log. - Check service overrides. Compare the global values in
main.cfwith-ooptions for the active service inmaster.cf. An override onsubmission,smtps, or another listener can make the effective limit differ from the global value.
Understand the Postfix limits that can create a fixed cadence
The controls below are per SMTP client unless their documentation says otherwise. “Client” may effectively mean an IP address, and authentication or service scope can affect how you observe the behavior. Read the parameter’s version-specific documentation before changing it.
| Parameter | What it counts | Documented default or qualification |
|---|---|---|
smtpd_client_message_rate_limit |
Message-delivery requests a client may make in the configured time interval | 0 (no limit) by default |
smtpd_client_connection_rate_limit |
New connections from a client in the interval | 0 (no limit) by default |
smtpd_client_connection_count_limit |
Simultaneous connections from a client | Check the effective value on the installed version |
smtpd_client_recipient_rate_limit |
Recipients a client may specify in the interval | 0 (no limit) by default |
smtpd_client_new_tls_session_rate_limit |
New TLS sessions from a client in the interval | Check the effective value on the installed version |
smtpd_client_auth_rate_limit |
AUTH commands from a client, where supported | Available only in newer Postfix versions; check your version’s reference |
smtpd_client_event_limit_exceptions |
Clients excluded from applicable event limits | The documented default exception list is $mynetworks |
Postfix’s own warning is important: “The purpose of this feature is to limit abuse. It must not be used to regulate legitimate mail traffic.” It appears in the postconf(5) reference. A limit should be narrowed or removed only after you know which client and event are affected; raising every control at once removes useful abuse protection and obscures the cause.
Why the pattern often looks like two per minute: anvil and its time window
The Postfix anvil service maintains the counters used by many of these client controls. The documented default for anvil_rate_time_unit is 60 seconds. The tuning guide describes the message limit as the maximum number of message-delivery requests an SMTP client may make during that interval; see Postfix TUNING_README.
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For example, a local setting of two message-delivery requests per 60-second window can appear exactly as “two emails per minute.” The same visual pattern can arise from a connection or recipient limit, so the log event must identify the rejected or deferred command before you change smtpd_client_message_rate_limit.
On a low-traffic system, anvil processes may pick up a main.cf change as they run. On other systems, postfix reload can speed adoption. A reload does not erase the need to verify the effective setting or prove that the relevant client is covered by an exception.
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Fix an inbound SMTP or client rate limit
Use this branch only when the log shows that the SMTP client request itself is being rejected or deferred. Record the baseline first: current parameter values, sender scope, queue size and age, and a timed test.
1. Identify the exact control
Match the log entry to the SMTP stage. A connection refusal or connection-rate message points to smtpd_client_connection_rate_limit; an AUTH event points to the AUTH limit where supported; a rejection after RCPT TO may indicate the recipient-rate control. A message-delivery event points to smtpd_client_message_rate_limit. If there is no explicit limit-related event, stop this branch and investigate the queue instead.
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2. Check the service-specific value
Inspect the active service in master.cf for an -o override. A submission service can enforce a value that is absent from the global main.cf output. Verify the service name and listener used by the application; changing the wrong service has no effect.
3. Decide whether the limit should be zero or narrowly higher
If the control is not needed for a trusted, authenticated submission path, set that particular parameter to 0 according to the documentation for your installed version. If abuse protection is still required, choose a measured nonzero value that accommodates the client’s workload instead of removing all limits. Do not change connection, recipient, TLS, and AUTH limits merely because one message limit was implicated.
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4. Review exceptions and network scope
smtpd_client_event_limit_exceptions defaults to $mynetworks. Confirm that the legitimate sender is actually in the intended mynetworks definition or is covered by a narrowly scoped exception. Do not add a broad address range without understanding that every host in it may bypass the applicable event limits and gain a more attractive abuse path.
5. Validate and reload
postfix check
postconf smtpd_client_message_rate_limit
postfix reloadReplace the parameter in the second command with the one you changed, and query the service-specific configuration as well when an override exists. postfix check catches configuration and permission problems; postconf confirms what Postfix will use; postfix reload asks running services to adopt the change.
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6. Repeat the controlled test
Send the same number of messages from the same client and record acceptance timestamps, SMTP responses, queue age, and remote-delivery results. A successful change should remove the specific reject or defer event without turning remote delivery problems into apparent SMTP success. Keep limits for untrusted clients and make any exception as narrow as the sender identity and network design permit.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When messages are accepted but delivery is slow
An SMTP 250-style acceptance means Postfix accepted responsibility for the message; it does not mean the recipient’s server accepted it. If the application receives acceptance and queue IDs accumulate, an smtpd or anvil limit is not established by the symptom alone.
Check queue age and delivery attempts
Run postqueue -p and follow several queue IDs in the mail log. Compare the time Postfix accepted each message with the first delivery attempt and with the most recent retry. A growing oldest-message age points toward queue scheduling, transport concurrency, retry or backoff behavior, or a blocked destination rather than an inbound client throttle.
Read the remote response
Look for temporary 4xx replies, destination-host rate deferrals, DNS lookup failures, connection timeouts, certificate or TLS negotiation errors, and provider-specific policy responses. Variable delays that track one recipient domain are different from a fixed local one-minute window. Resolve the remote condition before changing smtpd limits.
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Check concurrency and transport behavior
Review the transport handling the affected destination, its concurrency, and retry schedule. A server can accept messages quickly while deliberately making only a small number of outbound connections. Do not describe that behavior as anvil throttling unless the inbound SMTP logs show an anvil or smtpd event.
Could the application be creating the two-per-minute pattern?
Yes. An application that opens a new SMTP connection for each small message can hit connection controls, spend most of its time in TLS and authentication setup, or implement its own delay. The Postfix tuning guidance recommends submitting multiple recipients in one message when application privacy and message semantics allow it. It also recommends SMTP submission instead of repeatedly invoking /usr/sbin/sendmail for application traffic.
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- Batch recipients only when every recipient may legitimately receive the same message and disclosure requirements permit it.
- Measure connection setup, AUTH, message transmission, and server acceptance separately.
- Compare application timestamps with Postfix log timestamps; a gap before the SMTP connection is an application-side delay.
Batching is not a reason to ignore recipient privacy or consent. If each message must be individualized, keep separate messages but still reuse the submission connection where appropriate.
Quick Recap
Use a change-and-verify loop instead of guessing
- Capture a baseline: Postfix version, effective limits, active service, queue count, oldest queue age, representative log lines, and a timed controlled send.
- Classify the bottleneck: SMTP acceptance, queue scheduling, remote delivery, or application submission. Record whether it affects one IP or account or every sender, whether the cadence is fixed or variable, and whether a reject/defer line exists.
- Change one thing: modify only the implicated parameter or narrowly scoped exception. Keep the sender scope and rate window explicit in your change record.
- Validate syntax and effective values: run
postfix checkandpostconf; inspect the relevantmaster.cfservice override; then runpostfix reload. - Repeat identical traffic: use the same client, message size, recipient pattern, and test duration. Compare SMTP acceptance times, queue age, and remote responses with the baseline.
- Roll back if the evidence does not change: restore the previous value and continue in the branch indicated by the logs. A limit change that leaves acceptance events unchanged was probably aimed at the wrong layer.
Quick diagnosis matrix
| Observation | Most likely scope | Next check |
|---|---|---|
| Only one client IP receives a fixed-interval reject | Per-client smtpd limit or anvil counter | Relevant smtpd_client_* value, exceptions, and anvil log text |
| All clients on submission are slow, but port 25 behaves differently | Service-specific master.cf override |
Active service definition and every -o limit option |
| SMTP accepts immediately; queue age increases | Queue or outbound delivery | postqueue -p, queue IDs, destination responses, DNS, TLS, and retries |
| Delays vary by recipient domain | Remote deferral or destination policy | Remote SMTP status and per-domain delivery logs |
| Each message starts a new connection | Application-side overhead or connection-rate control | Client connection behavior, TLS/AUTH timing, and connection-rate setting |
| Configured count repeats every 60 seconds | Anvil time window | anvil_rate_time_unit and the specific counter being logged |
Common mistakes that make the problem worse
- Assuming two per minute is a Postfix default: the documented message, connection, and recipient rate defaults are zero; verify local configuration instead.
- Changing only
main.cf: a submission or smtps service may override the value inmaster.cf. - Disabling every limit: this removes abuse protection and makes a legitimate diagnosis harder. Correct the one control shown by the logs.
- Adding an unrestricted trusted network: the default exception is
$mynetworks; broadening it can expose the server to abuse. - Calling queued mail “rate-limited”: acceptance and remote delivery are separate events. Queue age and remote responses decide which branch applies.
- Testing with different traffic after the change: different recipients, message sizes, or client connections prevent a reliable before-and-after comparison.
What to retain from the diagnosis
- There is no documented universal Postfix limit of two emails per minute.
smtpd_client_message_rate_limit, connection-rate, and recipient-rate controls default to0; a nonzero local or service-specific value deserves scrutiny.anvil_rate_time_unitdefaults to 60 seconds, which can make a configured count look like a per-minute ceiling.smtpd_client_event_limit_exceptionsdefaults to$mynetworks, so the exact trusted-network scope matters.- An accepted message can still wait in the queue or be deferred by a remote host; SMTP acceptance is not final delivery.
- Service-specific
master.cfoverrides can differ from globalmain.cfvalues.
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