If you encounter this kind of error SMTP error 535 Authentication Failed while sending an email from Roundcube Webmail, then you can check the following things.

The error that probably you’ll see:
[text]SMTP error 535 authentication failed in roundcube
SMTP Error (435): Authentication failed[/text]

Open this file main.inc.php:

and change this line:
[text]$rcmail_config[‘smtp_user’] = ‘%u’;[/text]

into this:
[text]$rcmail_config[‘smtp_user’] = ”;[/text]
That’s it 😀

By zam

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4 thoughts on “535 authentication failed in Roundcube Webmail”
  1. Hello – thanks for this info. This is all new to me, I have just set up my email on roundcube and I’m suffering the same problem. How / where do I open file “main.inc.php”?

    1. That file is located in your roundcube folder inside config folder. Or if you want to search, you can try command “updatedb”, and then run command “locate main.inc.php” to search where the file is located.

  2. I’m having the same problem here. Although I’m using the webmail interface, so I have nothing installed on my PC to mess with.

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