Postfix "SASL authentication failure: No worthy mechs found"
Solution 1:
(New user, can't post comment reply to sebix. Also removed all links.)
For modern installations (such as Ubuntu 16.04) that use Postfix as an SMTP client with SASL-auth to a remote server (e.g. like shown on the Debian wiki), it might indeed be needed to specify
smtp_sasl_security_options = noanonymous
What this does, however, is remove the noplaintext option (currently the default is noplaintext, noanonymous as per the postconf manual). smtp_sasl_tls_security_options defaults to $smtp_sasl_security_options. This could become an issue under some (mis)configurations, or in the future if defaults change.
EDITED: At the moment, though, it doesn't seem likely, especially if SASL is done in a TLS session. This is forced if the remote server has smtpd_tls_auth_only or smtpd_enforce_tls (which implies the former) or whatever non-Postfix equivalent.
To check what Postfix defaults to, use postconf -d (via).
Solution 2:
this solved it for me (on centos 7 not default, was OK on older Centos versions)
yum install cyrus-sasl{,-plain}
service postfix restart
Solution 3:
It looks like the clue is right here:
untrusted issuer /C=US/O=Equifax/OU=Equifax Secure Certificate Authority
you need to get the equifax cert and add it to your list of trusted CA certs.
I think that these are available here: http://www.geotrust.com/resources/root-certificates/
Solution 4:
Possibly multiple problems here, the certs being one and another maybe related to smtp_sasl_security_options. I once solved a problem involving that "no mechs" message by setting smtp_sasl_security_options=noanonymous following a clue found on linuxquestions.org