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A free email verification API can catch malformed addresses and check whether a domain advertises mail routing, but those checks do not prove that a particular mailbox exists or that its owner controls it. A DEV Community project post by Aimly describes a Python and FastAPI API with those two checks, a stated allowance of 100 calls per day, and a claimed 10 ms response time. Those figures and features are the author’s claims, not independently verified results.
What the free API says it does
In a post published September 27, 2026, Aimly writes, “I built a simple email verification API using FastAPI + Python.” The post lists RFC 5322 format validation, MX record checking, 100 free calls per day, and a 10 ms response time. The project post links to a source repository and a demo, but neither was successfully inspected or tested for this article; current availability and behavior are therefore unconfirmed. Read Aimly’s project post.
The stated 100 calls per day is not identified as a per-user, per-key, per-IP, or global limit, and it has not been established that the limit is currently enforced. Likewise, 10 ms is the author’s response-time claim, not a published benchmark with test conditions.
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What an email check can establish
Syntax validation
A format check evaluates whether an address looks syntactically acceptable. The project post describes its check as RFC 5322 validation, but the code and tests were not independently reviewed, so standards-complete parsing is not established. A well-formed address can still point to a nonexistent mailbox.
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MX and domain-routing checks
SMTP uses DNS to locate a destination mail server. MX records commonly identify which servers receive mail for a domain; RFC 5321 also describes fallback to the domain’s address records when no MX record is present. This is information about domain-level routing, not proof that a particular mailbox exists, accepts messages, or belongs to the person entering it. RFC 5321: Simple Mail Transfer Protocol.
There is also a meaningful negative case: RFC 7505 defines a Null MX record as a signal that a domain does not accept email. An implementation should distinguish that explicit signal from an ordinary missing MX record, as well as from temporary DNS failures or timeouts. The project post’s visible comment discusses Null MX and DNS failures, but a comment is not evidence that the API handles those cases correctly. RFC 7505: A Null MX DNS Resource Record.
Choose the check that matches your goal
| Approach | What it observes | What it does not prove |
|---|---|---|
| Syntax-only validation | Whether the input appears to follow acceptable address formatting rules. | That the domain routes mail or that the mailbox exists. |
| Domain-routing check | DNS mail-routing information, such as MX records, with relevant fallback behavior described in RFC 5321. | That a specific mailbox exists, accepts mail, or is controlled by the submitter. |
| Confirmation message | Whether someone with access to the submitted mailbox can complete a confirmation flow. | That the address will remain deliverable indefinitely or that the person has any particular identity. |
The post describes format and MX checks. It does not establish that the project probes SMTP recipients or sends confirmation messages.
What to verify before using it in an application
Because the repository and demo have not been verified, the post alone does not establish the API’s route names, request and response format, authentication requirements, privacy practices, data retention, deployment region, uptime, error handling, or present-day availability. Confirm those details before sending user data or depending on the service in production.
- Check whether malformed input, a domain with Null MX, a missing MX record, DNS lookup failure, and timeout produce distinct, documented results.
- Determine how the stated daily allowance is counted and whether a key or other authentication is required.
- Review what address data is logged or retained, and whether the service’s privacy terms fit your use case.
- Test response behavior and latency under your own conditions rather than treating the post’s 10 ms claim as a service-level guarantee.
For basic input hygiene, syntax and DNS checks may help prevent obvious mistakes. If your workflow needs evidence that a person can access an address, use a confirmation flow. If you need dependable throughput, documented error semantics, or operational guarantees, evaluate a hosted service against those requirements instead of assuming this project provides them.
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