By Rupjyoti Nath | Updated 4 months ago | Email

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Legitmailbox Overview

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Rupjyoti Nath
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Verify if email actually exists.

Email Verification API to validate emails in real time. Detects whether an email is valid & deliverable without sending an email.

We send monthly summary/reports directly to your email.

Why use Email Verification API ?

  • Accept only valid emails during registration/newsletter signup forms.

  • Better communication: If a user mistakenly provides the wrong email, you will never be able to communicate.

  • Email Expires : Most of the employees change their jobs, so the emails are invalid now. For transactional emails, you may want to confirm the validity before sending.

  • Maintain reputation: Your email service provider might block you temporarily or permanently if there are too many hard bounces (bounces due to invalid emails)

What do we validate ?

  • Syntax: Whether it has a valid syntax.

  • MX Records: Does the domain have mail servers to receive email.

  • SMTP Ping : We reach the mail server to validate whether email exists.

  • Catch All: Some mail servers are configured in a way that it accepts any email in RCPT TO command, so we mark it as “catch_all”. It does not mean the email is invalid. Many legitimate organizations prefer this config to prevent revealing of the existence of email addresses.

  • Extras: We also provide details of whether the email is from a popular free email service . Also, whether the email is a well known role account, for example support@legitmailbox.com

Documentation (v1)

  • Verification endpoint
    Endpoint to verify email

    GET /api/v1/verify - Verifies the email provided

    Query string: email (required) - the email to verify
    Sample response:

    "message":"Invalid Syntax"

    Errors & Status Codes

    These are returned by our API. Additional status codes may be returned by RapidAPI itself.
    200 - OK
    400 - Bad Request (For invalid query parameters)
    401 - Unauthorized
    500 - For Internal server error

    Understanding Responses

    Here is a sample response,

        "professional" : true
        "role_account" : false
        "mx_records" : true
        "smtp_connection" : true
        "catch_all" : false
        "message" : "RCPT_TO_4XX"

    status: Can be “valid”, “invalid”, “unknown” or "catch-all"
    valid: Email exists and server is not catch-all server.

    invalid: Email does not exist or invalid as per the verification. You should not send emails to these addresses.

    unknown: We are unable to verify the status of the email. Probably because the email server is using grey-listing technology or it might be using some non standard code to convey the invalid status message.

    catch-all: Some mail servers accept any email provided in RCPT TO command. In such cases, it is not possible to know whether the email is valid or not. Also, a separate field “catch_all” will be marked true in such cases.

    syntax: true or false
    True for valid syntax, false otherwise

    professional: true if professional/custom domain email, false if well known free email provider. Helpful for B2B businesses to analyze or validate their signups & lead generation. Note that we only check the world’s popular free email providers only. Feel free to update us if we missed any popular webmail provider (free).

    role_account: true if the local part of email is associated with role accounts, for example support@ or contact@ , false if not. Helpful for B2B businesses to analyze or validate their signups & lead generation.

    mx_records: true if there is at least one MX record associated with the domain, false otherwise. No MX records means the domain cannot receive emails. If false, status will be “Invalid”.

    smtp_connection: Actually refers to TCP connection to the mail server (MX record). True if we are able to make a connection, false otherwise. If we are unable to make a connection to any mail servers (multiple MX), we mark the status as “Invalid” and “smtp_connection” will be false.

    catch_all: Some mail servers accept any email provided in RCPT TO command. In such cases, it is not possible to know whether the email is valid or not. “catch_all” will be marked true in such cases.

    message: This is used to provide more details/reason for “Invalid” & “Unknown” emails. You can debug the status/accuracy of the verification. In case of “Valid” emails, it may be an empty string.

    The “message” may also be in coded form such as 4XX_MAIL to reveal that we have received 4XX code when sending the MAIL FROM command.

    We will update the list of message codes that we may send in response.

    How to determine deliverability?

    If the “status” is “valid”, it actually means a 100% correct email address (as per the SMTP response and protocol). If status is “catch-all”, emails should be send to them as well as there are legitimate companies which use catch all configuration.

    If “status” is “invalid”, not deliverable. If “unknown”, we are not sure.

    List of possible “message” in verification response/result

    We provide a “message” field in our verification response. This helps you to debug the reason why an email was marked as “Invalid” or “Unknown”. In case of “Valid” status, this field may be an empty string.

    Here are few current messages related to SMTP VERIFICATION that we provide for “Invalid” or “Unknown” status:

    EHLO_ERROR : If an error occurs in the EHLO stage

    MAIL_FROM_ERROR : If an error occurs in MAIL FROM stage. This includes 4XX code received as well.

    RCPT_TO_ERROR : If an error occurs in RCPT TO stage. This is provided if we don’t get any standard SMTP response code.

    RCPT_TO_4XX : 4XX code received in RCPT TO response

    RCPT_TO_554 : 554 code received. Contact support if you see this code.

    RCPT_TO_550 but verify blocked by mail server : We got a 550 response but our IP may be blacklisted . Contact support if you see this message.

    MAILBOX_DISABLED_OR_FULL : The mailbox is disabled or full

    RCPT_TO_5XX cannot confirm if invalid : Received 5XX code but since different mail servers provide code and just a generic 5XX code cannot confirm the email status, we mark the status of email as “Unknown”

    We recommend our API subscribers to provide feedback to us regarding any particular message that you would want us to add in the response.
    Apart from the messages listed above, we provide other messages as well.


Can you verify any email?

Well, the SMTP verification depends on the recipient mail server. Some don’t provide accurate SMTP responses. Few are configured as Catch All servers.

Do you verify free email addresses?

We rely solely on SMTP verification. Some free email providers like Yahoo, Aol, Mail.ru are all Catch All servers. We cannot provide the accurate status. Other providers like Gmail, Rediffmail are not catch all, so we can accurately verify them.
Our best results are for professional email verifications.

Do I need credit card to try?

No, our Basic plan is free to use without providing payment information. Only when you want more verifications, you need to upgrade to a paid plan.<p></p>

Do you provide refunds?

No, we do not provide refunds.

Do you send emails to verify?

No, we do not send any email.

Do you perform SMTP verification using TLS?

When we perform SMTP verification with the mail server, we use Opportunistic TLS. This means, we use TLS (via STARTTLS) when the mail server supports STARTTLS. If the TLS connection succeeds, we perform the verification in a secure connection. However, if the TLS connection fails or STARTTLS is not supported, we will verify the email in plain text form.

We recommend our API subscribers to provide feedback to us regarding any custom TLS config/options that you would love to use, so we can change our existing product and modify according to your needs.

Here are a few questions that we have:
Do you want your email to be verified over TLS only ?


By Email : support@legitmailbox.com
For API integration problems or payment problems, support@rapidapi.com would be better.
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