all-in-one privacy solution":["Proton Unlimited è una soluzione completa per la privacy"],"Black Friday":["Black Friday"],"No ads. Privacy by default.":["Niente pubblicità. La prima regola è la privacy."],"People before profits":["Le persone prima dei profitti"],"Security through transparency":["Più sicurezza grazie alla trasparenza"],"The best Proton Mail ${ BLACK_FRIDAY } deals":["Le migliori offerte di Proton Mail per il ${ BLACK_FRIDAY }"],"The world’s only community- supported email service":["L'unico servizio di email al mondo supportato dalla community"]},"specialoffer:limited":{"${ hours } hour":["${ hours } ora","${ hours } ore"],"${ hoursLeft }, ${ minutesLeft } and ${ secondsLeft } left":["Restano ${ hoursLeft }, ${ minutesLeft } e ${ secondsLeft }"],"${ minutes } minute":["${ minutes } minuto","${ minutes } minuti"],"${ seconds } second":["${ seconds } secondo","${ seconds } secondi"],"Limited time offer":["Offerta a tempo limitato"]},"specialoffer:listitem":{"Create multiple addresses":["Crea indirizzi multipli"],"Hide-my-email aliases":["Alias hide-my-email"],"Quickly unsubscribe from newsletters":["Annulla rapidamente l'iscrizione alle newsletter"],"Use your own domain name":["Utilizza il tuo nome di dominio"]},"specialoffer:logos":{"As featured in":["Ne hanno parlato"]},"specialoffer:metadescription":{"Get an encrypted email that protects your privacy":["Scegli un'email cifrata per proteggere la tua privacy"]},"specialoffer:metatitle":{"Proton Mail Black Friday Sale - Up to 40% off":["Offerta Black Friday di Proton Mail - sconti fino al 40%"]},"specialoffer:newmetadescription":{"Get up to 40% off Proton Mail subscriptions this Black Friday. Find great deals on our secure end-to-end encrypted email plans.":["Per questo Black Friday ti offriamo fino al 40% di sconto sugli abbonamenti a Proton Mail. Scopri le straordinarie offerte sui piani di abbonamento alla nostra email dotata di crittografia end-to-end."]},"specialoffer:newmetatitle":{"Proton Mail Black Friday sale | Up to 40% off secure email":["Offerta di Proton Mail per il Black Friday | Fino al 40% di sconto sulla nostra email sicura"]},"specialoffer:note":{"* Billed at ${ TOTAL_SUM } for the first year":["* Addebito di ${ TOTAL_SUM } per il primo anno"],"*Billed at ${ TOTAL_SUM } for the first 2 years":["*Addebito di ${ TOTAL_SUM } per i primi 2 anni"],"30-day money-back guarantee":["Garanzia soddisfatti o rimborsati di 30 giorni"],"Billed at ${ TOTAL_SUM } for the first 2 years":["Addebito di ${ TOTAL_SUM } per i primi 2 anni"],"Billed at ${ TOTAL_SUM } for the first year":["Addebito di ${ TOTAL_SUM } per il primo anno"],"You save ${ SAVE_SUM }":["Risparmi ${ SAVE_SUM }"]},"specialoffer:off":{"${ PERCENT_OFF } off":["−${ PERCENT_OFF }"]},"specialoffer:testimonial":{"I love my ProtonMail":["Adoro ProtonMail"],"My favorite email service":["Il mio servizio email preferito"],"Thanks Proton for keeping us all safe in the complicated internet universe.":["Grazie Proton perché ci proteggi nell'universo complicato di internet."],"You get what you pay for. In the case of big tech, if you pay nothing, you get used. I quit using Gmail and switched to @ProtonMail":["Ottieni quello per cui hai pagato. Nel caso di big tech, se non paghi niente, vieni usato. Ho smesso di usare Gmail e sono passata a @ProtonMail"]},"specialoffer:time":{"Days":["Giorni"],"Hours":["Ore"],"Min":["Min"]},"specialoffer:title":{"And much more":["E altro ancora"],"Safe from trackers":["Protezione dai tracker"],"Stay organized":["Tieni tutto in ordine"],"Black Friday email deals":["Offerte email del Black Friday"],"Don’t just take our word for it":["Non lo diciamo solo noi"],"Make your inbox yours":["Rendi la tua posta in arrivo davvero tua"],"Our story":["La nostra storia"],"Transfer your data from Google in one click":["Trasferisci i tuoi dati da Google con un solo clic"]},"specialoffer:tooltip":{"Access blocked content and browse privately. Includes ${ TOTAL_VPN_SERVERS }+ servers in ${ TOTAL_VPN_COUNTRIES }+ countries, connect up to 10 devices, access worldwide streaming services, malware and ad-blocker, and more.":["Accedi a contenuti bloccati e naviga in modalità privata. Include oltre ${ TOTAL_VPN_SERVERS } server in più di ${ TOTAL_VPN_COUNTRIES } Paesi, possibilità di connettere fino a 10 dispositivi, accesso a servizi di streaming in tutto il mondo, anti-malware, ad-blocker e altro ancora."],"Easily share your calendar with your family, friends or colleagues, and view external calendars.":["Condividi facilmente il tuo calendario con familiari, amici o colleghi e visualizza calendari esterni."],"Includes support for 1 custom email domain, 10 email addresses, 10 hide-my-email aliases, calendar sharing, and more.":["Include il supporto per 1 dominio email personalizzato, 10 indirizzi email, 10 alias hide-my-email, condivisione del calendario e altro ancora."],"Includes support for 3 custom email domains, 15 email addresses, unlimited hide-my-email aliases, calendar sharing, and more.":["Include il supporto per 3 domini email personalizzati, 15 indirizzi email, alias hide-my-email illimitati, condivisione del calendario e altro ancora."],"Manage up to 25 calendars, mobile apps, secured with end-to-end encryption, 1-click calendar import from Google, and more.":["Gestisci fino a 25 calendari, app per dispositivi mobili, protezione con la crittografia end-to-end, importazione del calendario da Google in un solo clic e altro ancora."]},"Status banner":{"Learn more":["Scopri di più"],"Please note that at the moment we are experiencing issues with the ${ issues[0] } service.":["Attenzione: stiamo riscontrando dei problemi con il servizio di ${ issues[0] }"],"We are experiencing issues with one or more services at the moment.":["Stiamo riscontrando dei problemi con uno o più servizi."]},"Status Banner":{"At the moment we are experiencing issues with the Proton VPN service":["Al momento abbiamo dei problemi con il servizio di Proton VPN"],"Learn more":["Scopri di più"]},"steps":{"Step":["Passaggio"]},"suggestions":{"Suggestions":["Suggerimenti"]},"Support":{"Sub category":["Sottocategoria","Sottocategorie"]},"Support article":{"${ readingTime } min":["${ readingTime } minuto","${ readingTime } minuti"],"Category":["Categoria","Categorie"],"Didn’t find what you were looking for?":["Non hai trovato quello che cercavi?"],"General contact":["Contatti generali"],"Get help":["Ottieni supporto"],"Legal contact":["Contatti legali"],"Media contact":["Contatti per la stampa"],"Partnerships contact":["Contatti per collaborazioni"],"Reading":["Lettura"]},"Support Form Platform option":{"VPN for Android TV":["VPN per Android TV"],"VPN for Apple TV":["VPN per Apple TV"],"VPN for Chromebook":["VPN per Chromebook"]},"Support troubleshooting":{"App version":["Versione dell'app"],"Browser":["Browser"],"Check if this helps":["Verifica se questo ti è utile"],"Choose a product":["Scegli un prodotto"],"Did this solve your issue?":["Ha risolto il tuo problema?"],"Faster assistance is just a few clicks away":["Ottieni assistenza più velocemente con pochi clic"],"How can we help?":["Come possiamo aiutarti?"],"No, contact support":["No, contatta il supporto"],"Please fill out one field after another":["Compila un campo dopo l'altro"],"Please make your selections":["Fai la tua selezione"],"Proton account":["Account Proton"],"Proton for Business":["Proton for Business"],"Thank you for your feedback":["Grazie per il feedback"],"What can we help with?":["In cosa possiamo esserti di aiuto?"],"Yes":["Sì"]},"support_modal_search_query":{"Search query":["Query di ricerca"]},"support_search_button":{"Search":["Cerca"]},"support_search_i_am_looking_for":{"I'm looking for":["Sto cercando"]},"SupportForm":{"For a faster resolution, please report the issue from the Bridge app: Help > Report a problem.":["Per una risoluzione più rapida, segnala il problema dall'app Bridge: Aiuto > Segnala un problema."],"Information":["Informazioni"]},"SupportForm:option":{"Account Security":["Sicurezza dell'account"],"Contacts":["Contatti"],"Custom email domain":["Dominio email personalizzato"],"Email delivery and Spam":["Consegna delle email e spam"],"Encryption":["Crittografia"],"Login and password":["Login e password"],"Merge aliases and accounts":["Unione di alias e account"],"Migrate to Proton":["Migrazione a Proton"],"Notifications":["Notifiche"],"Other":["Altro"],"Plans and billing":["Piani e fatturazione"],"Proton for Business":["Proton for Business"],"Sign up":["Iscrizione"],"Storage":["Archiviazione"],"Users, addresses, and identities":["Utenti, indirizzi e identità"]},"SupportForm:optionIntro":{"Select a topic":["Seleziona un argomento"]},"Testimonial":{"Awards":["Premi"],"Customers":["Clienti"],"Featured":["In evidenza"],"Go to testimonial source":["Vai alle testimonianze"],"Open source of award":["Apri la fonte del premio"],"Open source of quote":["Apri la fonte della citazione"],"Reviews":["Recensioni"],"Videos":["Video"],"Watch on TikTok":["Guarda su TikTok"],"Watch on YouTube":["Guarda su YouTube"]},"TestimonialCategory":{"Awards":["Premi"],"Customers":["Clienti"],"Featured":["In evidenza"],"Media":["Media"],"Reviews":["Recensioni"],"Videos":["Video"]},"Text":{"If you need help, check out our ${ supportLink }.":["Se ti serve assistenza dai un’occhiata alla nostra ${ supportLink }."],"The page you’re looking for might have been removed, or it could be an\nold link.":["La pagina che stai cercando potrebbe essere stata rimossa, o il link potrebbe essere vecchio."],"Your question may already have an answer in our knowledge base:":["La risposta alla tua domanda potrebbe essere già disponibile nella nostra base di conoscenza:"]},"Title":{"On this page":["In questa pagina"],"Related articles":["Articoli correlati"],"Share ${ thisPage }":["Condividi ${ thisPage }"],"Switch to Proton Pass - Contact us":["Passa a Proton Pass - Contattaci"],"Thank you!":["Grazie"],"this page":["questa pagina"]},"tooltip_vpn":{"Access blocked content and browse privately. Includes ${ TOTAL_VPN_SERVERS }+ servers in ${ TOTAL_VPN_COUNTRIES }+ countries, highest VPN speed, ${ TOTAL_VPN_CONNECTIONS } VPN connections, worldwide streaming services, malware and ad-blocker, and more.":["Accedi a contenuti bloccati e naviga in modalità privata. Include oltre ${ TOTAL_VPN_SERVERS } server in più di ${ TOTAL_VPN_COUNTRIES } Paesi, VPN ad altissima velocità, ${ TOTAL_VPN_CONNECTIONS } connessioni VPN, servizi di streaming in tutto il mondo, anti-malware, ad-blocker e altro ancora."]},"vpn_servers":{"Get Proton VPN Plus":["Scegli Proton VPN Plus"]},"wallet_signup_2024:Action":{"Get Proton Wallet":["Ottieni Proton Wallet"]},"wallet_signup_2024:Homepage hero product link title":{"Wallet":["Wallet"]},"wallet_signup_2024:Homepage product navigation bar":{"Wallet":["Wallet"]},"wallet_signup_2024:menu item":{"Bitcoin guide":["Guida Bitcoin"],"Proton Wallet news":["Novità di Proton Wallet"],"Proton Wallet support":["Supporto di Proton Wallet"]},"wallet_signup_2024:Pricing":{"Includes everything in Proton Unlimited and":["Include tutte le funzionalità di Proton Unlimited e"],"Limited availability":["Disponibilità limitata"],"The easiest way to securely own, send, and receive Bitcoin":["Il modo più semplice di possedere, inviare e ricevere Bitcoin in modo sicuro"]},"wallet_signup_2024:ProductRange":{"Discover Proton Wallet":["Scopri Proton Wallet"],"Store and transact Bitcoin privately with an encrypted self-custody wallet.":["Conserva ed esegui transazioni in Bitcoin in modo privato con un portafoglio a custodia autonoma crittografato."]},"wallet_signup_2024:wallet bitcoin":{"Learn about Bitcoin, the Internet's value network.":["Scopri il Bitcoin, la rete di valore di Internet."]},"wallet_signup_2024:wallet overview":{"Ensure you're always in control of your Bitcoin.":["Assicurati di avere sempre il controllo dei tuoi Bitcoin."]},"wallet_signup_2024:wallet security":{"The encrypted, open-source wallet that puts you in control.":["Il portafoglio crittografato e open source che ti dà il controllo."]}}},"base":"support","cdn":{"enabledForAssets":true,"enabledForImages":false,"url":"https://pmecdn.protonweb.com/"},"unleashApi":"https://account.proton.me/api"};
window.frameworkContext = frameworkContext;
const context = frameworkContext.base === '' ? '' : `${frameworkContext.base}/`;
window.__toAssetUrl = (filename) => {
if (frameworkContext.cdn !== undefined && frameworkContext.cdn.enabledForAssets === true) {
return `${frameworkContext.cdn.url}${context}${filename}`;
} else {
return `/${context}${filename}`;
}
};
})();
SMTP (Simple Mail Transfer Protocol) is a standard internet protocol that mail servers use to send and receive emails. If a mail server can’t send an email, it replies with an SMTP error message.
SMTP error messages are messages mail servers send if an incoming or outgoing message bounces. They provide valuable information about why the message wasn’t delivered successfully.
Reviewing the SMTP error code in the bounce message can help you diagnose and resolve the issue.
What do SMTP error messages look like?
SMTP error messages are generally made up of three parts:
1. Reply code
2. Status code
3. Description
xyz Example: 550
x.y.z Example: 5.1.1
Example: “The email account that you tried to reach does not exist.”
Each digit (x, y, and z) in the reply and status codes indicates extra detail about the error.
Here’s an example of an SMTP error message:
SMTP reply codes refer to different aspects of the email service and can indicate issues such as:
The intended recipient’s email address is not registered with the service.
The message has been marked as spam or flagged for containing a virus.
The sender’s domain has been identified as a source of spam.
The email message violates the company’s email policy, such as containing sensitive information like credit card numbers or using prohibited language.
Not all SMTP reply codes indicate errors. Reply codes starting with a “4” or “5” are errors.
Types of SMTP error codes
Errors in SMTP are categorized into two main groups based on the starting digit of the reply code:
Error codes starting with a “4” indicate temporary failures: No immediate action is needed, and the sender’s mail server will automatically retry sending the email.
Error codes starting with a “5” indicate permanent failures: Action is required to resolve the issue and successfully deliver the email.
Understanding and responding to SMTP error codes can help quickly resolve email delivery problems.
For further assistance on email delivery issues, please send us the details of your error using our support form(nuova finestra).
Common SMTP 400 error codes
Error code
SMTP error message
Explanation
421
4.3.0 Temporary System Problem. Try again later.
Temporary issue on the server side; asking the sender to retry later.
421
4.4.5 Server busy, try again later.
The server is currently overloaded; requesting the sender to retry later.
421
4.7.0 IP not in whitelist for RCPT domain, closing connection.
The sending IP address isn’t authorized to send emails to the recipient domain.
421
4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address.
The sending IP address has been blocked temporarily due to suspected spamming.
421
4.7.0 Temporary System Problem. Try again later.
Temporary issue on the server side; asking the sender to retry later.
421
4.7.0 TLS required for RCPT domain, closing connection.
The recipient domain requires TLS encryption for email transmission.
421
4.7.0 Try again later, closing connection. This usually indicates a DoS for the SMTP relay at the HELO stage.
Denial of Service (DoS) attack on the SMTP relay during the initial handshake.
450
4.2.1 The user you are trying to contact is receiving mail too quickly. Please resend your message later.
The recipient’s mailbox is temporarily overloaded; asking the sender to try again later.
450
4.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages.
The recipient is receiving emails too quickly, and further messages are delayed.
450
4.2.1 Peak SMTP relay limit exceeded for this customer. This is a temporary error.
The maximum number of SMTP relays has been reached, causing a temporary error.
451
4.3.0 Mail server temporarily rejected message.
Temporary rejection of the message by the recipient’s mail server.
451
4.3.0 Multiple destination domains per transaction are unsupported. Please try again.
Attempt to send emails to multiple domains in a single transaction, which isn’t supported.
451
4.4.2 Timeout – closing connection.
The server closed the connection due to a timeout.
451
4.5.0 SMTP protocol violation, visit RFC 2821.
The SMTP protocol was violated during the exchange of commands.
452
4.2.2 The email account that you tried to reach is over quota.
The recipient’s mailbox is full and cannot accept more messages.
452
4.5.3 Domain policy size per transaction exceeded, please try this recipient in a separate transaction.
The email policy size for the recipient domain has been exceeded.
452
4.5.3 Your message has too many recipients.
The message has too many recipients, and the server can’t process it in a single transaction.
454
4.5.0 SMTP protocol violation, no commands allowed to pipeline after STARTTLS, visit RFC 3207.
A violation of the SMTP protocol occurred after initiating TLS encryption.
454
4.7.0 Cannot authenticate due to temporary system problem. Try again later.
Temporary issue preventing authentication; asking the sender to retry later.
454
5.5.1 STARTTLS may not be repeated.
Attempting to restart TLS encryption when it’s not allowed.
Common SMTP 500 error codes
Error code
SMTP error message
Explanation
501
5.5.2 Cannot Decode response.
The server can’t decode the response from the client.
501
5.5.4 HELO/EHLO argument is invalid.
Invalid argument provided during the HELO/EHLO stage of SMTP.
502
5.5.1 Too many unrecognized commands, goodbye.
The server received too many unrecognized commands and terminates the connection.
502
5.5.1 Unimplemented command.
The server received an unimplemented command and terminates the connection.
502
5.5.1 Unrecognized command.
The server received an unrecognized command and terminates the connection.
503
5.5.1 EHLO/HELO first.
The client should send the EHLO/HELO command first before any other commands.
503
5.5.1 MAIL first.
The client should send the MAIL command before the RCPT command.
503
5.5.1 RCPT first.
The client should send the RCPT command after the MAIL command.
503
5.7.0 No identity changes permitted.
The server doesn’t allow changes to the message sender identity.
504
5.7.4 Unrecognized Authentication Type.
The server doesn’t recognize the authentication type used by the client.
530
5.5.1 Authentication Required.
Authentication is required to send emails through the server.
530
5.7.0 Must issue a STARTTLS command first.
The client must issue the STARTTLS command before attempting to authenticate.
535
5.5.4 Optional Argument not permitted for that AUTH mode.
An optional argument isn’t allowed for the specified authentication mode.
535
5.7.1 Application-specific password required.
An application-specific password is required for authentication.
535
5.7.1 Please log in with your web browser and then try again.
The user must log in through the web browser to resolve authentication issues.
535
5.7.1 Username and Password not accepted.
The provided username and password aren’t accepted for authentication.
550
5.1.1 The email account that you tried to reach does not exist.
The recipient’s email address doesn’t exist or is misspelled.
550
5.2.1 The email account that you tried to reach is disabled.
The recipient’s email account is disabled and can’t receive messages.
550
5.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages.
The recipient is receiving emails too quickly, and further messages are delayed.
550
5.4.5 Daily sending quota exceeded.
The sender has exceeded their daily email sending quota.
550
5.4.5 Daily SMTP relay limit exceeded for user.
The sender has exceeded their daily SMTP relay limit.
550
5.7.0 Mail relay denied.
The server has denied mail relay for the sender’s IP address.
550
5.7.1 Email quota exceeded.
The recipient’s email account has exceeded its quota and can’t receive more messages.
550
5.7.1 Invalid credentials for relay.
The provided credentials for SMTP relay are invalid.
550
5.7.1 Our system has detected an unusual rate of unsolicited mail from your IP address.
The sender’s IP address has been blocked due to suspected spamming.
550
5.7.1 Our system has detected that this message is likely unsolicited mail.
The message has been blocked as it appears to be spam.
550
5.7.1 The IP you’re using to send mail is not authorized to send email directly to our servers.
The sender’s IP isn’t authorized to send emails directly to the recipient’s server.
550
5.7.1 The user or domain you are sending to (or from) has a policy that prohibited the mail that you sent.
The recipient domain has a policy that blocked the sent email.
550
5.7.1 Unauthenticated email is not accepted from this domain.
The server doesn’t accept unauthenticated emails from the specified domain.
550
5.7.1 Daily SMTP relay limit exceeded for customer.
The sender has exceeded their daily SMTP relay limit.
550
5.7.26 Unauthenticated email from domain-name is not accepted due to the domain’s DMARC policy.
The domain’s DMARC policy is blocking unauthenticated emails.
552
5.2.2 The email account that you tried to reach is over quota.
The recipient’s mailbox is full and can’t accept more messages.
552
5.2.3 Your message exceeded Google’s message size limits.
The message size exceeds the maximum allowed by Google’s email service.
553
5.1.2 We weren’t able to find the recipient domain.
The recipient domain doesn’t exist or has a typo in the email address.
554
5.6.0 Mail message is malformed. Not accepted.
The email message is malformed and can’t be accepted.
554
5.6.0 Message exceeded 50 hops, this may indicate a mail loop.
The message has passed through too many servers, suggesting a mail loop.
554
5.7.0 Too Many Unauthenticated commands.
The server received too many unauthenticated commands and terminates the connection.
555
5.5.2 Syntax error.
The server encountered a syntax error in the client’s command.