Saslauth Failed (curl easy perform error)

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Saslauth Failed (curl_easy_perform error)

   KB 24091        Last updated on 2021-11-15  

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IMAP/POP clients get a password pop-up window and are not able to send and receive any e-mails. When using the correct username and password, the following authentication error in /var/log/zimbra.log file is observed :

Nov 28 15:06:57 mbox1 saslauthd[45799]: auth_zimbra: auth failed: curl_easy_perform: error(56): Received HTTP code 503 from proxy after
Nov 28 15:06:57 mbox1 saslauthd[45799]: do_auth         : auth failure: [] [service=smtp] [] [mech=zimbra] [rea
Nov 28 15:06:57 mbox1 postfix/smtpd[18938]: warning: unknown[]: SASL LOGIN authentication failed: authentication failure
Nov 28 15:06:57 mbox1 postfix/smtpd[18938]: lost connection after AUTH from unknown[]


Check if any additional forward proxy is enabled (like Nginx or Squid)

Run following command to check the additional proxy:

# env | grep -i proxy

Run the following command to check saslauth with the mailbox node. The same curl command works in the backend during saslauth.

$ curl -X POST -u -d 'authType=sasl' -k

Remove additional proxy and restart the MTA service to invalidate the old saslauth connection which was established.

$ zmmtactl restart

Why does this issue occur?

When saslauth happens on MTA server, it checks ZCS saslauthd lookup server on port 7073 which is a mailbox server. If a local forward proxy is configured, this request will be handled by this proxy. Since this proxy doesn't know where to forward this request to, it shows HTTP 503 and 502 errors.

How SASL works

SASL is not a protocol but is a framework that can be used with protocols such as SMTP. For each protocol that uses SASL, there will be a specification as to how the protocol uses SASL. This means that SASL can be used with a wide range of protocols, and can be adapted to the details of how any specific protocols work.

The basic operation of SASL is straightforward. The server provides a list of supported authentication mechanisms, and then the client says which one will be used (based on the client’s capabilities and security requirements).

Protocols that contain SASL support include:

  • LDAP (Internet Standard Lightweight Directory Access Protocol)
  • SMTP (Internet Standard Simple Message Transfer Protocol)
  • POP3 (Internet Standard Post Office Protocol v3)
  • IMAP (Internet Standard Internet Mail Access Protocol)
  • XMPP: Extensible Messaging and Presence Protocol
  • Isode's SOM (Switch Operations and Management) Protocol

This external link contains more information about SASL.

Submitted by: Gopal Singh Bhandari
Verified Against: ZCS 8.8 Date Created: 2020-04-13
Article ID: Date Modified: 2021-11-15

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