Can't send email

This error can appear when trying to send email from Email section or when user registers:

We're sorry, but something went wrong.
We've been notified about this issue and we'll take a look at it shortly.

• Check GUI log
• Try with Default settings

Default settings

• SMTP Server: smtp.gmail.com
• Domain: localhost.localdomain
• Login: kolmitest
• Password: kolmitest99
• Batch Size: 50

Errors

Net::SMTPAuthenticationError (535 invalid user ID or password)

On both of these errors:

1. Check your SMTP server details
2. Try to use another SMTP server
3. Try default settings:

SMTP Server: smtp.gmail.com 
Domain: localhost.localdomain
Login: kolmitest
Password: kolmitest99

NameError (undefined local variable or method `xxxxxx' for #)

Do not add variables which are not from this list:

• <%= server_ip %>
• <%= device_type %>
• <%= device_username %>
• <%= device_password %>
• <%= login_url %>
• <%= login_username %>
• <%= login_password %>
• <%= username %>
• <%= first_name %>
• <%= last_name %>
• <%= full_name %>

Timeout::Error (execution expired) /usr/lib/ruby/1.8/timeout.rb:54:in `open'

Open port 25 to allow SMTP connection.

OpenSSL::SSL::SSLError (unknown protocol)

No solution yet...

SocketError (getaddrinfo: Name or service not known)

Execute (on Debian):

apt-get install mime-construct
mime-construct --to "your@mail.com" --subject 'hi there' --string "body"

Go to /var/log/exim4/mainlog

If you see:

2008-04-14 08:35:06 1JlOMs-0001fU-I4 <= root@GUI.cantv.net U=root P=local S=404
2008-04-14 08:35:12 1JlOMs-0001fU-I4 ** your@mail.com R=dnslookup T=remote_smtp: SMTP error from remote mail server after end of data: host gmail-smtp-in.l.google.com [64.233.185.27]:  550-5.7.1 [190.37.134
.234] The IP you're using to send mail is not authorized\n550-5.7.1 to send email directly to our servers. Please use the SMTP\n550-5.7.1 relay at your service provider instead. Learn  more at\n550 5.7.1 http:
//mail.google.com/support/bin/answer.py?answer=10336 7si13749186wrl.12

That means you should use your providers SMTP server to send emails.