Postfix: SASL authentication failed Email / SMTP Origin: Network Last updated 4 Nov 2026

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 are not set up correctly.

Exact message you may see warning: SASL authentication failure: cannot connect to saslauthd serverSASL authentication failed; cannot authenticate to serverSASL LOGIN authentication failed: authentication failurewarning: SASL authentication failure: No worthy mechs foundpostfix/smtp SASL authentication failed
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Seen on: SMTP Linux

Meaning

For inbound auth, Postfix asks Dovecot or saslauthd; the socket path or chroot must match. For a relayhost login, the sasl_passwd file must be hashed with postmap and have the exact [host]:port key. The log line right after the warning shows the specific cause.

Common causes

  • saslauthd not running or socket missing (chroot path)
  • Dovecot auth socket not exposed to Postfix
  • sasl_passwd not hashed with postmap
  • Key in sasl_passwd does not match relayhost exactly
  • Missing SASL library (libsasl2-modules)

⚡ Quick fix

  1. Start saslauthd/Dovecot and verify the socket path
  2. Run postmap /etc/postfix/sasl_passwd and restart
  3. Install libsasl2-modules for plain/login mechanisms

Detailed fix by platform

Linux

  1. sudo apt-get install -y libsasl2-modules && sudo postmap /etc/postfix/sasl_passwd && sudo chmod 600 /etc/postfix/sasl_passwd* && sudo systemctl restart postfix

How to diagnose

  1. Direction — Inbound or relay login?
  2. Socket — SASL service up?
  3. Hash — postmap rebuilt?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

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 Authenticat…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 Application…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 an…IMAP: Too many simultaneous connections — IMAP: NO [ALERT] Too many simultaneous connections. (Failure) (Email / SMTP)IMAP: Too many simult…Nodemailer: EAUTH Invalid login — Nodemailer: Error: Invalid login: 535-5.7.8 Username and Password not accepted (code: 'EAUTH', responseCode: 535) (Email / SMTP)Nodemailer: EAUTH Inv…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: bind 0.0.0.0…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 doma…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=defer…Postfix: …

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