I recently would like to configure my wordpress site to send mail through SMTP plugin. But I always faced the Authentication Failed error when using zoho smtp server. There is no problem using gmail in configuring wordpress SMPT.

The following is the error log when the Authentication Failed error happens:

2015-11-07 10:15:54	SERVER -> CLIENT: 250-mx.zohomail.com Hello hugeproxies.com (ec2-52-89-206-160.us-west-2.compute.amazonaws.com (52.89.206.160))
                   	                  250-AUTH LOGIN PLAIN
                   	                  250 SIZE 25000000
2015-11-07 10:15:54	Auth method requested: UNKNOWN
2015-11-07 10:15:54	Auth methods available on the server: LOGIN,PLAIN
2015-11-07 10:15:54	Auth method selected: LOGIN
2015-11-07 10:15:54	CLIENT -> SERVER: AUTH LOGIN
2015-11-07 10:15:54	SMTP -> get_lines(): $data was ""
2015-11-07 10:15:54	SMTP -> get_lines(): $str is "334 xxxxxxxxxxxxxxxxxxxxx
                   	                  "
2015-11-07 10:15:54	SMTP -> get_lines(): $data is "334 xxxxxxxxxxxxxxxxxxxx
                   	                  "
2015-11-07 10:15:54	SERVER -> CLIENT: 334 xxxxxxxxxxxxxxxxxx
2015-11-07 10:15:54	CLIENT -> SERVER: xxxxxxxxxxxxxxxxxxxxxx=
2015-11-07 10:15:54	SMTP -> get_lines(): $data was ""
2015-11-07 10:15:54	SMTP -> get_lines(): $str is "334 xxxxxxxxxxxxxxxxxxx
                   	                  "
2015-11-07 10:15:54	SMTP -> get_lines(): $data is "334 xxxxxxxxxxxxxxxx
                   	                  "
2015-11-07 10:15:54	SERVER -> CLIENT: 334 xxxxxxxxxxxxxxxxx
2015-11-07 10:15:54	CLIENT -> SERVER: xxxxxxxxxxxxxxxxxxx==
2015-11-07 10:15:54	SMTP -> get_lines(): $data was ""
2015-11-07 10:15:54	SMTP -> get_lines(): $str is "535 Authentication Failed
                   	                  "
2015-11-07 10:15:54	SMTP -> get_lines(): $data is "535 Authentication Failed
                   	                  "
2015-11-07 10:15:54	SERVER -> CLIENT: 535 Authentication Failed
2015-11-07 10:15:54	SMTP ERROR: Password command failed: 535 Authentication Failed
2015-11-07 10:15:54	SMTP Error: Could not authenticate.
2015-11-07 10:15:54	CLIENT -> SERVER: QUIT
2015-11-07 10:15:54	SMTP -> get_lines(): $data was ""
2015-11-07 10:15:54	SMTP -> get_lines(): $str is "221 mx.zohomail.com closing connection
                   	                  "
2015-11-07 10:15:54	SMTP -> get_lines(): $data is "221 mx.zohomail.com closing connection
                   	                  "
2015-11-07 10:15:54	SERVER -> CLIENT: 221 mx.zohomail.com closing connection
2015-11-07 10:15:54	Connection: closed 

2015-11-07 10:15:54 SMTP Error: Could not authenticate. 

I've tried both SSL and TLS configuration stated in https://www.zoho.com/mail/help/zoho-smtp.html, both failed. Can someone help me to solve the problem? Thanks.

Daniel