Error map
452 4.5.3 Too many recipients SMTP: 452 4.5.3 Your message has too many recipients / 452 Too many recipients received this hour
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)
fork: retry: Resource temporarily unavailable (process/thread limit)
The user or container hit its maximum number of processes/threads (ulimit -u, pids cgroup), so new processes can’t be created.
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
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.
IMAP: NO [ALERT] Too many simultaneous connections. (Failure)
The server limits concurrent IMAP sessions per account and your clients (phone, laptop, scripts) opened more than allowed.
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.
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: 452 4.2.2 The email account that you tried to reach is over quota
The recipient's mailbox has exceeded its storage quota, so the server will not accept new mail for now.
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: 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.
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.
Two steps away (29)
Error: listen EADDRINUSE: address already in use :::3000
Another process is already listening on that port.
Error: write EPIPE
Node wrote to a pipe or socket whose other end was already closed.
RangeError [ERR_CHILD_PROCESS_STDIO_MAXBUFFER]: stdout maxBuffer length exceeded
child_process.exec/execSync produced more output than its buffer allows (default 1 MB).
Error: ENOENT: no such file or directory
A file or directory the program tried to open doesn’t exist at that path.
Error: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
MySQL ERROR 1040 (08004): Too many connections
MySQL reached `max_connections` and refuses new clients.
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…
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…
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).
Postfix: warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory
Postfix could not authenticate a user (inbound) or could not log in to a relay (outbound) because the SASL service or credentials…
IMAP: NO [AUTHENTICATIONFAILED] Invalid credentials (Failure)
The IMAP server rejected the login — wrong password, IMAP disabled, an app password required, or basic auth blocked.
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…
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: 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: 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: 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…
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.
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…
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`.
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.
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: [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…
Laravel: Expected response code "250" but got code "550", with message "550 5.7.1 Relaying denied"
Laravel connected and authenticated but the SMTP server rejected the message at the RCPT TO / MAIL FROM / DATA step with the code…
SMTP: 554 5.7.1 Message content rejected / Your message looks like spam (spam score exceeded)
The receiver's content filter scored your message as spam based on its text, links, headers or sender reputation and rejected it…
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