SMTP Error Codes
SMTP Error Codes by Email Provider
Every mailbox provider writes its own bounce text. These pages collect the exact SMTP responses recorded from Gmail, Outlook, Yahoo, Apple iCloud, Zoho and more, so you can match your bounce to a specific fix.
All email providers
- Apple5 codesicloud.com, me.com, mac.comApple provides iCloud Mail for icloud.com, me.com and mac.com addresses. There is little self-service tooling, so anything beyond following its published guidance needs a message to its postmaster team.
- AT&T1 codeatt.net, sbcglobal.net, swbell.net, bellsouth.netAT&T operates mail for att.net, sbcglobal.net, bellsouth.net and related legacy domains. It runs a postmaster site with a route for disputing spam verdicts.
- Comcast5 codescomcast.netComcast, branded Xfinity, gives comcast.net mailboxes to its internet customers. Accounts go inactive after roughly 90 days without a sign-in, so these addresses age out over time.
- Free3 codesFreeFree is a French ISP that provides mailboxes to its customers. Its postmaster pages document error codes and IP lookups and explain how to report a wrong spam verdict.
- GMX3 codesGMXGMX is a German free-mail provider, part of the same group as Mail.com. European receivers weight GDPR compliance heavily, and a listing on a recognised allowlist can help delivery.
- Google7 codesgmail.com, googlemail.comGoogle runs Gmail for consumers and Google Workspace for businesses. Filtering is almost entirely automated with very little human review, so senders should watch domain reputation and performance in Google Postmaster Tools rather than expect a support conversation.
- Hey1 codeHeyHEY is a paid mail service from 37signals. It screens senders per recipient, so there is little a sender can do to influence delivery because each recipient decides which addresses they accept.
- Hostpoint1 codeHostpointHostpoint is a Swiss host that runs mail for domains registered with it.
- ImprovMX3 codesImprovMXImprovMX is an email forwarding service that receives mail on a custom domain and passes it to a personal inbox. Its rejections are documented in a public error-code guide.
- Infomaniak2 codesInfomaniakInfomaniak is a Swiss hosting company that runs mail for domains registered with it. Rejections generally follow standard SPF, DKIM and DMARC checks.
- Mail.ru1 codemail.ruMail.ru is a large Russian ISP and mail provider with firm published sending rules, including a ban on link shorteners. Registering sending domains with its postmaster tools gives direct reputation data.
- Orange3 codesOrangeOrange is a French ISP that offers free mailboxes to customers and registered non-customers. Once the mail is confirmed legitimate, false-positive blocks can be reported to Orange's abuse team.
- Outlook7 codeshotmail.com, outlook.com, msn.com, live.comOutlook covers the consumer hotmail.com, outlook.com, live.com and msn.com addresses that sit under Microsoft. Legitimate mail landing in junk usually needs a sender support request, while an IP-level block has to be appealed by whoever controls the IP.
- ProtonMail1 codeProtonMailProton Mail is a Swiss provider and the largest host of end-to-end encrypted email.
- QQ2 codesQQQQ Mail is Tencent's mail service in China. Delivery from senders and servers outside China can be unpredictable, so registering the Return-Path domain with QQ's postmaster site is the best way to get visibility.
- Rackspace1 codeRackspaceRackspace Email is a hosted mailbox product for businesses, with spam filtering, firewall and blocklist features and an unusually detailed public postmaster site.
- Rambler3 codesRamblerRambler is a Russian search and mail provider. There is no dedicated postmaster site, so misclassified mail is disputed with its abuse team.
- Web.de1 codeWeb.deWeb.de is a German free-mail provider. As with other European receivers, GDPR compliance and allowlist status carry weight.
- Yahoo Inc9 codesyahoo.com, aol.com, verizon.netYahoo handles mail for the yahoo.com, aol.com and verizon.net families. It publishes clear sender requirements and offers a postmaster site plus a complaint feedback loop for investigating misclassified mail.
- Yandex7 codesyandex.comYandex is a Russian search and mail provider with strict published rules on opt-in and unsubscribe handling. Its public postmaster tools were retired after abuse, so troubleshooting means contacting its abuse team directly.
- Zoho6 codeszoho.comZoho Mail is the mail product inside Zoho's business software suite, with its own spam filtering, firewall and blocklist controls.
