How to fix SMTP authen fail with error "curl_easy_perform: error(56)"

When SMTP authentication fails in Zimbra for every user and program, check the error log at /var/log/zimbra.log. You may find an error like this:

Jul 28 16:34:05 server saslauthd[33294]: authentication against url ’ https://s1.ezymailhosting.com:7071/service/admin/soap’ caused error ‘curl_easy_perform: error(56): Received HTTP code 403 from proxy after CONNECT’

Cause SMTP authentication in Zimbra fails for every user and program because a proxy is configured at the OS level, preventing the system from connecting to the mailboxd service on port 7071. Checking the problem Test access to the mailbox service on Port 7071 with:

[root@S1 ~]# wget -d --no-check-certificate https://s1.ezymailhosting.com:7071

If the result is “Proxy tunneling failed: Method Not AllowedUnable to establish SSL connection.”, as in the example below, a proxy is indeed configured at the OS level.

---request end---
proxy responded with: [HTTP/1.1 405 Method Not Allowed
Date: Sun, 28 Jul 2013 16:36:20 GMT
Content-Length: 235
Connection: close
Content-Type: text/html; charset=iso-8859-1
X-Squid-Error: ERR_ACCESS_DENIED 0
X-Cache: MISS from proxy.ezymailhosting.com
X-Cache-Lookup: NONE from proxy.ezymailhosting.com:8080
Via: 1.0 proxy.ezymailhosting.com (squid/3.0.STABLE24)
Proxy-Connection: close

]
Proxy tunneling failed: Method Not AllowedUnable to establish SSL connection.

Fixing the problem Check /opt/zimbra/.bashrc or /etc/bashrc for HTTPS_PROXY or ALL_PROXY. If either is present, remove it immediately and restart the saslauthd service with:

[root@S1 ~]# su - zimbra
[zimbra@S1 ~]$ zmsaslauthdctl restart