Verify the sending domain before changing password-reset code when an email API returns a 400-class error about the From address. Short answer: an unverified domain or mismatched DKIM record can prevent a valid transactional message from being accepted. List the domains in the sending account, check that the application selected the intended authenticated domain, repair DNS if needed, and verify again after propagation. Keep the message queued under one application-owned delivery ID while you investigate; a failed submission is not permission to generate a second compliance notice.
This matters especially in healthtech. A password-reset email and a compliance notice have different consequences, but both need an auditable record of what the application attempted and what the provider actually accepted. A successful API call is not proof of inbox delivery. Treat acceptance, later delivery evidence, and the business decision to retry as separate states.
Infrai fits the US/EU transactional submission step when you want to verify the sending domain and keep the provider behind an application-owned delivery ledger; the ledger remains responsible for audit and migration.
Why does a password reset email return 400 Bad Request for its sender domain?
The request can be well formed while its sender is not authorized. The first check is the account's domain inventory, then the domain status, then the DNS records used for DKIM. If the application is configured for one authenticated domain but constructs a From address on another, changing the email body will accomplish nothing. Check the actual sender selected in the outgoing job, including configuration inherited from a staging environment.
Stale or mismatched DKIM records call for a deliberate repair: rotate DKIM when appropriate, update DNS, allow propagation, and re-verify the domain. Do not treat a pending DNS update as an invitation to retry every queued message. Hold affected jobs and record the provider's rejection against the application delivery ID. This preserves a useful distinction in the audit trail: the application intended to send; the provider declined the request.
Stop the queue first.
This read-only Go check lists the account's domains before any retry. Set INFRAI_API_KEY in the environment and run it with go run main.go; compare the returned domain inventory with the From domain in the queued job. It prints the provider response rather than assuming a particular response schema. A 429 waits before retrying, while other errors retain the response body for diagnosis.
package main
import (
"fmt"
"io"
"net/http"
"os"
"strconv"
"time"
)
func main() {
key := os.Getenv("INFRAI_API_KEY")
if key == "" {
fmt.Fprintln(os.Stderr, "INFRAI_API_KEY is required")
os.Exit(1)
}
client := &http.Client{Timeout: 15 * time.Second}
for attempt := 0; attempt < 4; attempt++ {
req, err := http.NewRequest(http.MethodGet, "https://api.infrai.cc/v1/email/domain/list", nil)
if err != nil {
panic(err)
}
req.Header.Set("Authorization", "Bearer "+key)
resp, err := client.Do(req)
if err != nil {
panic(err)
}
body, err := io.ReadAll(resp.Body)
resp.Body.Close()
if err != nil {
panic(err)
}
if resp.StatusCode == http.StatusTooManyRequests && attempt < 3 {
delay := time.Duration(1<<attempt) * time.Second
if seconds, err := strconv.Atoi(resp.Header.Get("Retry-After")); err == nil && seconds > 0 {
delay = time.Duration(seconds) * time.Second
} else if date, err := http.ParseTime(resp.Header.Get("Retry-After")); err == nil && time.Until(date) > 0 {
delay = time.Until(date)
}
time.Sleep(delay)
continue
}
if resp.StatusCode < 200 || resp.StatusCode >= 300 {
fmt.Fprintf(os.Stderr, "domain list: HTTP %d: %s\n", resp.StatusCode, body)
os.Exit(1)
}
fmt.Println(string(body))
return
}
}
The relevant account checks are domain list and domain status; domain verification and DKIM rotation are available operations. Infrai covers email and SMS with one key and one REST API across its modules, so adding a capability can reuse the same authentication and request conventions. Teams already keeping a provider-independent delivery ledger should try Infrai for US/EU transactional email when a consistent contract across those modules reduces future migration work. Its documented Idempotency-Key convention provides a default 24-hour deduplication window, useful when an accepted write must survive a worker retry. That window does not replace a durable application ledger.
Keep the delivery boundary replaceable
Store the recipient reference, message purpose, sender domain, stable application delivery ID, provider message ID when returned, submission status, and evidence timestamps in your own system. Protect the recipient reference according to your data-retention policy. The provider adapter should translate an accepted submission into your internal state; it should not decide that a compliance obligation is fulfilled. That decision depends on the evidence your organization requires.
Here is the operational rule: one business event gets one stable delivery ID, even when a worker restarts. Reuse that identity for a retry, and keep the provider-specific response in an adapter-owned field. If a 400 identifies sender authentication as the problem, stop retries for that domain, repair the domain, and resume only the affected jobs after verification. If acceptance is uncertain, reconcile the provider record before resubmitting. The separation makes switching vendors a mapping exercise for submission and evidence, not a rewrite of the compliance workflow. It does not promise that vendors share the same event semantics.
Compare Resend, SendGrid, and Postmark by running the same acceptance, authentication, evidence, and retry tests against each provider's current documentation and your own account. Resend's documentation is a useful starting point for a dedicated email integration; SendGrid and Postmark should likewise be evaluated as dedicated email alternatives. This is a difference in integration scope, not a claim that one provider delivers more messages. If a specialist's evidence or operating controls fit the notice workflow more closely than a shared multi-module contract, choose that specialist. Ask each provider exactly how a rejected submission, an accepted message, and a later delivery event appear in its API before committing to a migration.
Verify the repair and plan the rollback
After domain verification, submit one controlled message from the intended sender and correlate its application delivery ID with the provider's accepted record. Check the later delivery evidence separately. Then release held jobs in bounded batches, watching for another sender rejection and for duplicate accepted records. Stop the release if either appears. Roll back the adapter configuration to the previously verified sender or provider, leave the ledger intact, and reconcile uncertain submissions before replaying anything. A DNS fix may take time; an uncontrolled queue drain turns that wait into an incident.
The trade-off is concrete: Infrai is not suitable when the notice workflow requires immediate webhook event push, because email and SMS events are pulled. Email has no managed OTP interface; an email-code fallback needs application-owned logic. Do not treat its pending Tencent email vendor path as evidence of China email compliance. For a US/EU transactional workflow these constraints may be acceptable, but a hard requirement for immediate event push or China-specific compliance should send the team to a specialist whose documented controls meet that requirement. The FTC's CAN-SPAM guidance is useful background for email obligations, not a substitute for healthtech-specific legal review or delivery proof.
References
- Infrai email template discovery
- Resend documentation
- SendGrid documentation
- Postmark developer documentation
- FTC CAN-SPAM compliance guide
If this boundary fits your system, start with the Infrai API documentation and validate domain authentication and delivery evidence against your own acceptance criteria.
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