Error map

Postfix: bind 0.0.0.0 port 25: Address already in use Postfix: fatal: bind 0.0.0.0 port 25: Address already in use

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
Postfix: bind 0.0.0.0 port 25: Address already in use — Postfix: fatal: bind 0.0.0.0 port 25: Address already in use (Email / SMTP)Postfix: bi…Postfix: status=deferred (connect ... Connection timed out) — Postfix: status=deferred (connect to gmail-smtp-in.l.google.com[142.250.27.26]:25: Connection timed out) (Email / SMTP)Postfix: status=def…Postfix: Host or domain name not found — Postfix: status=deferred (Host or domain name not found. Name service error for name=example.com type=A: Host not found, try again) (Email / SMTP)Postfix: Host or do…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…Postfix: SASL authentication failed — Postfix: warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory (Email / SMTP)Postfix: SASL authe…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…Outbound port 25 blocked — SMTP: telnet smtp.example.com 25 — Connection timed out (cloud provider blocks port 25) (Email / SMTP)Outbound port 25 bl…554 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…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…DKIM: no key for signature — DKIM: dkim=permerror (no key for signature) / key not found in DNS selector._domainkey (Email / SMTP)DKIM: no key for si…DMARC: no record found — DMARC: dmarc=none (no DMARC record found for example.com) — bulk sender requirements not met (Email / SMTP)DMARC: no record fo…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 5.7.26452 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…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 …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 Message s…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…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…535 5.7.8 Username and Password not accepted — SMTP: 535-5.7.8 Username and Password not accepted. Learn more at https://support.google.com/mail/?p=BadCredentials (Email / SMTP)535 5.7.8 Username …550 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…ssh port 22 Connection timed out — ssh: connect to host x port 22: Connection timed out (Linux)ssh port 22 Connect…No route to host — connect: No route to host (EHOSTUNREACH) (Linux)No route to hostConnectionRefusedError [Errno 111] (SMTP) — Python: ConnectionRefusedError: [Errno 111] Connection refused — smtplib connect to localhost:25 (Email / SMTP)ConnectionRefusedEr…

Directly related (7)

Postfix: status=deferred (connect ... Connection timed out)Email / SMTP

Postfix: status=deferred (connect to gmail-smtp-in.l.google.com[142.250.27.26]:25: Connection timed out)

Postfix could not reach the remote mail server on port 25, so the message stays in the queue and is retried.

Postfix: Host or domain name not foundEmail / SMTP

Postfix: status=deferred (Host or domain name not found. Name service error for name=example.com type=A: Host not found, try again)

Postfix could not resolve the destination domain through DNS — the resolver is down or unreachable, or the domain does not exist.

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…

Postfix: SASL authentication failedEmail / SMTP

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…

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.

Outbound port 25 blockedEmail / SMTP

SMTP: telnet smtp.example.com 25 — Connection timed out (cloud provider blocks port 25)

Connections from your server to other mail servers on port 25 time out because your cloud host or ISP blocks outbound SMTP to fig…

Two steps away (19)

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…

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…

DKIM: no key for signatureEmail / SMTP

DKIM: dkim=permerror (no key for signature) / key not found in DNS selector._domainkey

The message is signed with a selector, but the receiver found no DKIM public key in DNS at that selector, so verification cannot…

DMARC: no record foundEmail / SMTP

DMARC: dmarc=none (no DMARC record found for example.com) — bulk sender requirements not met

The sender's domain publishes no `_dmarc` TXT record, so receivers cannot apply any policy; Gmail and Yahoo now require one for b…

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).

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.

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.

552 5.3.4 Message size exceeds fixed limitEmail / SMTP

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.

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.

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…

535 5.7.8 Username and Password not acceptedEmail / SMTP

SMTP: 535-5.7.8 Username and Password not accepted. Learn more at https://support.google.com/mail/?p=BadCredentials

The server received your login but rejected it — wrong username or password, an unusable password type, or a blocked sign-in.

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.

ssh port 22 Connection timed outLinux

ssh: connect to host x port 22: Connection timed out

SSH packets get no reply — a firewall/security group drops them, the server is off, or the IP is wrong.

No route to hostLinux

connect: No route to host (EHOSTUNREACH)

The destination host isn’t reachable — it’s down, on another subnet without routing, or a firewall rejects with “host unreachable…

ConnectionRefusedError [Errno 111] (SMTP)Email / SMTP

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…

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