can not send email - SMTP error on roundcube

[Telepuzik]

I know this is old post and marked as not resolved, but, digging around I found a solution which resolved my issue with SMTP error:

I have modified this file:

/etc/sentora/configs/roundcube/roundcube_config.inc.php


replace this line:

$config['smtp_user'] = '%u';

to

$config['smtp_user'] = '';

and replace this line:

$config['smtp_password'] = '%p';

to 

$config['smtp_password'] = '';

// NOTE: '' is TWO ' , and this is not a single " symbol.

Spent 2 weeks re-installing and modifiying configs, but by the end, changes above fixed "smtp error (535) authentication failed" issue.... Yay.... Hope it will help others.