Domain Intelligence
Last Updated:

Costco.com

Safe to Send

Costco.com is operated by Costco Wholesale. The domain runs 2 mail exchanges and SMTP is responsive, with all three authentication standards in force.

Safe to Send
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Verify @costco.com emails

Live SMTP handshake against costco.com mail servers. No email is sent. 10 free per day, no signup.

@costco.com
No email sent No signup Real-time SMTP

Trusted by 400,000+ senders

4.9/5
From 8,500+ verified reviews
Reached out to support during our API integration last month. Response in under 15 minutes, the rep was so sharp and helpful that by the end of the thread it honestly felt like I was flirting with him. Amazing support team. A+++. Nathan Orozco · Lead Engineer · via X
SOC 2 Type II GDPR CCPA 99.7% Accuracy
Disposable
No
Persistent addresses, not throwaway
SMTP Live
Yes
Mail server responds to SMTP handshake
MX Records
2
Mail exchangers

Mail Exchange (MX) Records for costco.com Mail Exchange records. They tell other mail servers which hosts are responsible for receiving email at this domain, in priority order. Lower priority numbers are tried first.

2 RECORDS
#10
mx0b-001f9d01.pphosted.com 148.163.158.49
Reachable
#10
mx0a-001f9d01.pphosted.com 148.163.156.53
Reachable
SMTP Handshake Simple Mail Transfer Protocol. We open a live SMTP connection to the primary MX and read the greeting banner. A response confirms the mail server is alive and accepting connections. Responsive
BANNER220 mx0b-001f9d01.pphosted.com ESMTP mfa-m0374081
Primary mail server accepted SMTP connection and returned a banner during the live audit.

costco.com Email Authentication SPF · DKIM · DMARC

3/3 PASS
SPF Sender Policy Framework. A DNS record listing which servers are allowed to send mail for this domain. Receivers reject or flag mail from unauthorized servers. Pass
TXTv=spf1 include:%{ir}.%{v}.%{d}.spf.has.pphosted.com -all
Authorized senders are defined and pass SPF policy.
DKIM DomainKeys Identified Mail. The sending server cryptographically signs outbound mail with a private key, and receivers verify the signature using a public key in DNS. Pass
SELECTORDetected via standard selectors
A DKIM signature was detected. Outbound mail from this domain can be cryptographically verified.
DMARC Domain-based Message Authentication, Reporting & Conformance. Tells receivers what to do when SPF or DKIM checks fail: none, quarantine, or reject. Reject
TXTv=DMARC1; p=reject; fo=1; rua=mailto:dmarc_rua@emaildefense.proofpoint.com; ruf=mailto:dmarc_ruf@emaildefense.proofpoint.com;
Strict policy. Receivers are instructed to reject any mail that fails SPF or DKIM. The strongest available setting.

costco.com Domain Registration WHOIS · Nameservers · Registrar

29 YEARS OLD
RegistrarCSC Corporate Domains, Inc.
IANA ID299
RegisteredMarch 16, 1997
Last UpdatedApril 24, 2026
ExpiresMarch 18, 2027
Age29 years
TLD.com
Authoritative Nameservers (6)
  • a28-66.akam.net
  • a14-67.akam.net
  • a1-116.akam.net
  • a9-66.akam.net
  • a5-64.akam.net
  • a6-64.akam.net
Registrant
Costco Wholesale Membership, Inc.
WA, UNITED STATES
About this Domain

About costco.com

Costco Wholesale (costco.com) is the world's third-largest retailer and the largest membership-only warehouse club chain, headquartered in Issaquah, Washington. Costco operates over 860 warehouses worldwide and serves more than 120 million cardholders. The company is known for its bulk-quantity merchandising model and consistently ranks among the most trusted retailers.

Costco implements enterprise email authentication on the costco.com domain with SPF, DKIM, and DMARC protocols. As a major retailer with a large membership base, Costco is targeted by phishing campaigns impersonating membership renewals, exclusive deals, and executive communications. Authentication protects the brand from domain spoofing.

SMTP verification of costco.com addresses returns definitive responses for valid and invalid mailboxes. The domain does not function as catch-all. Costco's mail infrastructure implements rate limiting on inbound SMTP connections.

For suppliers and business partners communicating with Costco employees, proper sender authentication is important. Costco's corporate email filters check incoming messages for SPF, DKIM, and DMARC compliance. Full authentication compliance helps ensure reliable delivery to costco.com addresses.

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Common Questions About costco.com

Is costco.com a disposable or temporary email provider?
No. costco.com is not a disposable email provider. It is classified as Corporate Email operated by Costco Wholesale and addresses on costco.com are persistent rather than throwaway. Mail sent to a valid costco.com mailbox reaches a real recipient.
How do I verify if a costco.com email address is valid?
The fastest way to verify a costco.com email address is to use our free email checker. Enter any @costco.com mailbox at the top of this page and our system performs a real-time SMTP handshake against costco.com's mail servers, confirming whether the mailbox exists, is reachable, and is safe to send to. No email is ever delivered during the check.
Can I check if a costco.com email exists without sending a message?
Yes. Our real-time email verification API connects directly to costco.com's mail server, opens an SMTP session, and queries the mailbox using the RCPT TO command without ever transmitting an actual email. The server's response confirms whether the costco.com mailbox is valid, full, or non-existent. The recipient never receives anything and never sees the check.
What are the MX records for costco.com?
costco.com currently publishes 2 mail exchange (MX) records. The primary MX is mx0b-001f9d01.pphosted.com, which is the first server contacted when other mail systems try to deliver email to a costco.com address. The full list with priorities and IP addresses is in the MX Records panel above. MX records tell sending servers where to route email for costco.com.
Does costco.com use SPF, DKIM, and DMARC email authentication?
costco.com enforces all three email authentication standards: SPF, DKIM, and DMARC (policy: reject). This is the gold-standard configuration. It means receivers can verify that mail claiming to come from @costco.com is genuine, and costco.com's DMARC policy of 'reject' instructs receivers how to handle messages that fail those checks.
Why do emails to costco.com bounce or get blocked?
Bounces from costco.com usually fall into three buckets: the mailbox doesn't exist (5xx user unknown), the inbox is full, or your sending domain isn't authenticated to costco.com's satisfaction. The fastest fix is to run each address through a free email verifier before you send, and to make sure your own SPF, DKIM, and DMARC are configured correctly so costco.com's receivers trust you.
How can I verify a large list of costco.com email addresses?
Our bulk email verifier accepts CSV or TXT uploads with thousands or millions of costco.com addresses (or any mix of domains). Every address goes through 30+ checks including SMTP existence, costco.com catch-all detection, role-account detection, and disposable-domain matching. Results typically come back within minutes and previously-failed addresses on your blacklist are reprocessed for free. For continuous high-volume needs, see our unlimited email verification API.
Is it safe to accept signups from costco.com email addresses?
Yes, with normal hygiene. costco.com is a legitimate email service and signups from @costco.com behave like any other real user. Pipe each address through a real-time email verifier API at the moment of signup to catch typos and dead mailboxes, but there is no need to block costco.com by default.
What email format does costco.com use for usernames?
Most costco.com mailboxes follow common patterns like first.last@costco.com, firstinitiallast@costco.com, or first@costco.com, but the actual local-part rules depend on Costco Wholesale. The only reliable way to confirm whether a specific @costco.com address exists is to run it through a free email verification tool. Guessing patterns will produce a high bounce rate and damage your sender reputation.
How is the costco.com risk score calculated?
The 0-to-100 risk score for costco.com combines disposable-domain classification, mail-server reachability, MX record presence and depth, SPF / DKIM / DMARC enforcement, DMARC policy strength, SMTP banner response, and domain age. Lower scores mean safer to send to. Disposable domains are pinned at the high end of the scale. The costco.com score is recomputed on every audit so it always reflects the live state of the domain.
Is costco.com a valid email domain?
Yes, costco.com is the official corporate email domain for Costco Wholesale. It is used for business communications and is not available for public registration.
Is costco.com a disposable or temporary email provider?
No, costco.com is a corporate email domain belonging to Costco Wholesale, used exclusively by employees and authorized personnel.
What mail server does costco.com use?
costco.com uses enterprise-grade mail infrastructure. Check the MX records section above for specific mail server details.
Can I send marketing emails to costco.com addresses?
B2B marketing to costco.com addresses requires proper consent and compliance with anti-spam laws. Corporate domains may use catch-all configurations, so verify addresses before sending.
How do I verify an email address at costco.com?
Corporate domains like costco.com may use catch-all configurations. Use BulkEmailChecker advanced verification to detect catch-all behavior and validate individual addresses.