Error map

552 5.3.4 Message size exceeds fixed limit SMTP: 552 5.3.4 Message size exceeds fixed maximum message size

Email / SMTP · layer 2, Network

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Centre: this error. First ring: errors it is linked with (7). 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.

2 · Network 4 · Application & API 6 · Platform & cloud
552 5.3.4 Message size exceeds fixed limit — SMTP: 552 5.3.4 Message size exceeds fixed maximum message size (Email / SMTP)552 5.3.4 M…530 5.7.0 Authentication Required — SMTP: 530 5.7.0 Must issue a STARTTLS command first / 530 5.7.1 Authentication required (Email / SMTP)530 5.7.0 Authentic…421 4.7.0 Try again later (rate limited) — 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 (Email / SMTP)421 4.7.0 Try again…450 4.7.1 Greylisted, please try again later — SMTP: 450 4.7.1 <user@example.com>: Recipient address rejected: Greylisted, see http://postgrey.schweikert.ch/help/example.com.html (Email / SMTP)450 4.7.1 Greyliste…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)452 4.2.2 Mailbox f…554 5.7.1 Service unavailable; client host rejected — 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 (Email / SMTP)554 5.7.1 Service u…451 4.3.0 Local error in processing — SMTP: 451 4.3.0 Error: queue file write error / 451 Requested action aborted: local error in processing (Email / SMTP)451 4.3.0 Local err…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)452 4.5.3 Too many …NOAUTH — ReplyError: NOAUTH Authentication required. (Node.js)NOAUTHToo many authentication failures — Received disconnect: Too many authentication failures (Linux)Too many authentica…Authentication token manipulation error — passwd: Authentication token manipulation error (Linux)Authentication toke…SMTP Error: Could not authenticate — WordPress / PHPMailer: SMTP Error: Could not authenticate / SMTP connect() failed (WordPress)SMTP Error: Could n…550 5.7.1 — 550 5.7.1 Relaying denied / Message rejected as spam / Unauthenticated email not accepted (Email / SMTP)550 5.7.1550 5.7.26 — 550 5.7.26 This mail has been blocked because the sender is unauthenticated (SPF/DKIM/DMARC) (Email / SMTP)550 5.7.26550 5.7.1 Blocked using zen.spamhaus.org — SMTP: 550 5.7.1 Service unavailable; Client host [203.0.113.5] blocked using zen.spamhaus.org (Email / SMTP)550 5.7.1 Blocked u…550 5.4.1 Recipient address rejected: Access denied — SMTP: 550 5.4.1 Recipient address rejected: Access denied. AS(201806281) [DB5EUR03FT015.eop-EUR03.prod.protection.outlook.com] (Email / SMTP)550 5.4.1 Recipient…553 5.7.1 Sender address rejected: not owned by user — SMTP: 553 5.7.1 <noreply@example.com>: Sender address rejected: not owned by user user@example.com (Email / SMTP)553 5.7.1 Sender ad…550 5.1.1 — 550 5.1.1 The email account that you tried to reach does not exist (User unknown) (Email / SMTP)550 5.1.1554 5.4.14 Hop count exceeded - possible mail loop — SMTP: 554 5.4.14 Hop count exceeded - possible mail loop (Email / SMTP)554 5.4.14 Hop coun…SMTPServerDisconnected: Connection unexpectedly closed — Python: smtplib.SMTPServerDisconnected: Connection unexpectedly closed (Email / SMTP)SMTPServerDisconnec…550 5.7.25 PTR record required — 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 (Email / SMTP)550 5.7.25 PTR reco…Helo command rejected: need fully-qualified hostname — SMTP: 504 5.5.2 <localhost>: Helo command rejected: need fully-qualified hostname (Email / SMTP)Helo command reject…534 5.7.9 Application-specific password required — SMTP: 534-5.7.9 Application-specific password required. Learn more at https://support.google.com/accounts/answer/185833 (Email / SMTP)534 5.7.9 Applicati…550 5.4.5 Daily user sending quota exceeded — SMTP: 550 5.4.5 Daily user sending quota exceeded (Gmail) (Email / SMTP)550 5.4.5 Daily use…SSL: WRONG_VERSION_NUMBER (SMTP port) — SMTP: [SSL: WRONG_VERSION_NUMBER] wrong version number — SMTP over SSL on a STARTTLS port (Email / SMTP)SSL: WRONG_VERSION_…EMFILE — Too many open files (EMFILE) (Linux)EMFILEfork: retry: Resource temporarily unavailable — fork: retry: Resource temporarily unavailable (process/thread limit) (Linux)fork: retry: Resour…IMAP: Too many simultaneous connections — IMAP: NO [ALERT] Too many simultaneous connections. (Failure) (Email / SMTP)IMAP: Too many simu…

Directly related (7)

530 5.7.0 Authentication RequiredEmail / SMTP

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.

421 4.7.0 Try again later (rate limited)Email / SMTP

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…

450 4.7.1 Greylisted, please try again laterEmail / SMTP

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…

452 4.2.2 Mailbox full / over quotaEmail / SMTP

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.

554 5.7.1 Service unavailable; client host rejectedEmail / SMTP

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.

451 4.3.0 Local error in processingEmail / SMTP

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.

452 4.5.3 Too many recipientsEmail / SMTP

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.

Two steps away (20)

NOAUTHNode.js

ReplyError: NOAUTH Authentication required.

The Redis server requires a password (or ACL user) but the client didn’t authenticate.

Too many authentication failuresLinux

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).

Authentication token manipulation errorLinux

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 Error: Could not authenticateWordPress

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 5.7.1Email / SMTP

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 5.7.26Email / SMTP

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).

550 5.7.1 Blocked using zen.spamhaus.orgEmail / SMTP

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.

550 5.4.1 Recipient address rejected: Access deniedEmail / SMTP

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…

553 5.7.1 Sender address rejected: not owned by userEmail / SMTP

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.

550 5.1.1Email / SMTP

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.

554 5.4.14 Hop count exceeded - possible mail loopEmail / SMTP

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…

SMTPServerDisconnected: Connection unexpectedly closedEmail / SMTP

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…

550 5.7.25 PTR record requiredEmail / SMTP

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…

Helo command rejected: need fully-qualified hostnameEmail / SMTP

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.

534 5.7.9 Application-specific password requiredEmail / SMTP

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…

550 5.4.5 Daily user sending quota exceededEmail / SMTP

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…

SSL: WRONG_VERSION_NUMBER (SMTP port)Email / SMTP

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…

EMFILELinux

Too many open files (EMFILE)

The process hit its file-descriptor limit — sockets, files and pipes all count.

fork: retry: Resource temporarily unavailableLinux

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.

IMAP: Too many simultaneous connectionsEmail / SMTP

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.

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