Error map
452 4.2.2 Mailbox full / over quota SMTP: 452 4.2.2 The email account that you tried to reach is over quota
Email / SMTP · layer 2, Network
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
550 5.1.1 The email account that you tried to reach does not exist (User unknown)
The recipient mailbox doesn’t exist on the receiving server — a typo in the address, a deleted account, or a wrong domain.
Laravel: Symfony\Component\Mailer\Exception\TransportException: Connection could not be established with host "smtp.mailtrap.io:2525": stream_socket_client(): Unable to connect
Laravel's mailer could not connect to the SMTP host configured in `.env`.
Mailgun: 403 Forbidden — Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authorized recipients
You are sending from Mailgun's free sandbox domain, which only delivers to addresses you have manually authorized.
SMTP: 421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address. Mail sent from your IP address has been temporarily rate limited
The receiving server (often Gmail or Outlook) is temporarily throttling your mail because the volume or reputation of your sendin…
SMTP: 450 4.7.1 <user@example.com>: Recipient address rejected: Greylisted, see http://postgrey.schweikert.ch/help/example.com.html
The recipient server deliberately rejected the first delivery attempt from an unknown sender (greylisting) and expects a legitima…
SMTP: 552 5.3.4 Message size exceeds fixed maximum message size
The message, including attachments after base64 encoding, is larger than the receiving or sending server accepts.
SMTP: 554 5.7.1 Service unavailable; Client host [203.0.113.5] blocked / 554 5.7.1 <mail.example.com>: Client host rejected: Access denied
The server refused the connection from your IP because it is blocked by policy, not in the allowed list, or listed on a blacklist.
SMTP: 554 5.4.14 Hop count exceeded - possible mail loop
The message passed through too many mail servers (usually over 25), which almost always means two systems forward mail to each ot…
SMTP: 530 5.7.0 Must issue a STARTTLS command first / 530 5.7.1 Authentication required
The server will not accept mail until you encrypt the connection (STARTTLS) and/or authenticate, and your client did neither.
Python: smtplib.SMTPServerDisconnected: Connection unexpectedly closed
The server closed the connection before your script finished the SMTP conversation — a timeout, blocked IP, TLS mismatch or rate…
PHP: sh: 1: /usr/sbin/sendmail: not found — mail() returns false
PHP's `mail()` calls the `sendmail_path` program, but it is not installed or the path in php.ini is wrong.
SMTP: 451 4.3.0 Error: queue file write error / 451 Requested action aborted: local error in processing
The server hit an internal problem (disk, database, content filter, DNS) while handling your message and asked you to retry later.
Two steps away (32)
PHP mail() returns false / emails not delivered
PHP’s mail() function failed or emails never arrive (spam or rejected).
SES MessageRejected: Email address is not verified. The following identities failed the check in region
SES refused to send because the From address/domain isn’t verified — or the account is still in the SES sandbox, where recipients…
Contact Form 7: There was an error trying to send your message. Please try again later.
The form submitted, but wp_mail() failed to send — the server can’t send mail or the mail settings are wrong.
Laravel: No application encryption key has been specified.
Laravel’s APP_KEY is missing, so it can’t encrypt sessions and cookies.
Laravel: 419 Page Expired (CSRF token mismatch)
Laravel rejected a POST because the CSRF token was missing, expired or didn’t match the session.
Laravel: Target class [App\Http\Controllers\X] does not exist.
Laravel’s container couldn’t find the controller or class named in a route or binding.
DMARC: dmarc=fail (p=REJECT) — SPF and DKIM pass but domains are not aligned with the From header
Authentication passed for another domain (your ESP's), but neither the SPF Return-Path domain nor the DKIM `d=` domain matches th…
SendGrid: 403 Forbidden — The from address does not match a verified Sender Identity. Mail cannot be sent until this error is resolved
SendGrid only sends from addresses or domains you have verified (single sender or domain authentication).
Amazon SES: Throttling — Maximum sending rate exceeded (454 Throttling failure)
You are sending faster than your Amazon SES account's per-second limit, so SES throttles the requests.
WordPress / PHPMailer: SMTP Error: Could not authenticate / SMTP connect() failed
The SMTP server rejected the login or couldn’t be reached — wrong credentials, app passwords required, wrong port/encryption, or…
550 5.7.1 Relaying denied / Message rejected as spam / Unauthenticated email not accepted
The receiving (or your outgoing) mail server refused the message — relaying isn’t allowed, the sender isn’t authenticated, or it…
550 5.7.26 This mail has been blocked because the sender is unauthenticated (SPF/DKIM/DMARC)
Gmail/Outlook rejected the message because SPF and DKIM didn’t pass for the sender’s domain (DMARC failure).
SMTP: 452 4.5.3 Your message has too many recipients / 452 Too many recipients received this hour
The server limits how many recipients a single message or sender may have; yours exceeded it.
SMTP: 550 5.7.1 Service unavailable; Client host [203.0.113.5] blocked using zen.spamhaus.org
The receiving server checked your IP in a DNS blocklist (Spamhaus, Barracuda, SORBS…) and refused your mail because it is listed.
SMTP: 550 5.4.1 Recipient address rejected: Access denied. AS(201806281) [DB5EUR03FT015.eop-EUR03.prod.protection.outlook.com]
Microsoft 365 / Exchange Online rejected the message because the recipient address does not exist in that tenant (Directory Based…
SMTP: 550-5.7.25 The IP address sending this message does not have a PTR record setup, or the corresponding forward DNS entry does not point to the sending IP
Gmail (and others) require your sending IP to have a reverse DNS (PTR) record that resolves back to the same IP; yours has none o…
SMTP: 504 5.5.2 <localhost>: Helo command rejected: need fully-qualified hostname
The receiving server refused your EHLO/HELO greeting because the name you sent is not a valid fully-qualified domain name.
TypeError: Missing parameter name at 1 (path-to-regexp)
An Express 5 (path-to-regexp v8) route uses old wildcard syntax like '*' or '/:id?'.
connect: Network is unreachable (ENETUNREACH)
The host has no route to the destination network — no default gateway, interface down, or trying IPv6 without IPv6 connectivity.
WordPress REST API: {"code":"rest_no_route","message":"No route was found matching the URL and request method."}
The REST endpoint doesn’t exist for that URL and HTTP method — wrong namespace/route, plugin not active, or route registered too…
ReplyError: NOAUTH Authentication required.
The Redis server requires a password (or ACL user) but the client didn’t authenticate.
Received disconnect: Too many authentication failures
Your SSH agent offered too many keys before the right one, and the server cut the connection (MaxAuthTries, default 6).
passwd: Authentication token manipulation error
passwd couldn’t update the password — the root filesystem is read-only, /etc/shadow has wrong permissions/attributes, or a PAM ru…
SMTP: [SSL: WRONG_VERSION_NUMBER] wrong version number — SMTP over SSL on a STARTTLS port
Your client tried to start TLS immediately on a port where the server speaks plain SMTP first (or the reverse), so the handshake…
Python: smtplib.SMTPAuthenticationError: (535, b'5.7.8 Username and Password not accepted')
`smtp.login()` was rejected by the server — wrong credentials, wrong password type, or authentication not allowed for that accoun…
Python: ConnectionRefusedError: [Errno 111] Connection refused — smtplib connect to localhost:25
Nothing is listening on the SMTP host and port your script connected to — often `localhost:25` because no host was given and no l…
WordPress: Your PHP installation appears to be missing the MySQL extension which is required by WordPress
PHP doesn’t have the mysqli extension loaded, so WordPress can’t talk to the database.
WordPress: Your server is running PHP version 7.2 but WordPress 6.x requires at least 7.4 / This plugin requires a newer version of PHP
WordPress core, a plugin or a theme needs a newer PHP than the server runs.
PHPMailer: SMTP Error: Could not connect to SMTP host. Failed to connect to server (SMTP connect() failed)
PHPMailer could not open a socket to the SMTP server — wrong host/port/encryption, a blocked port, or a PHP/OpenSSL restriction.
SMTP: 553 5.7.1 <noreply@example.com>: Sender address rejected: not owned by user user@example.com
The SMTP server only lets an authenticated user send as addresses they own, and the From/envelope sender does not match the login.
SMTP: 534-5.7.9 Application-specific password required. Learn more at https://support.google.com/accounts/answer/185833
The Google account has 2-Step Verification on, so SMTP clients cannot use the normal password; they need an app password (or OAut…
SMTP: 550 5.4.5 Daily user sending quota exceeded (Gmail)
The Gmail or Google Workspace account reached its 24-hour sending limit, so it stops accepting outgoing mail until the limit rese…
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