==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.2
- Linux/BSD distribution name and version: Ubuntu 14.04.2
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro? Yes
- Related log if you're reporting an issue:
====

Hello.
I'm trying to connect a Java application to send emails connecting with my iredmail server.

I have tested the application using Gmail and it sends without problems.
Configuration for gmail:

grails {
   mail {
     host = "smtp.gmail.com"
     port = 465
     username = "youracount@gmail.com"
     password = "yourpassword"
     props = ["mail.smtp.auth":"true",                       
              "mail.smtp.socketFactory.port":"465",
              "mail.smtp.socketFactory.class":"javax.net.ssl.SSLSocketFactory",
              "mail.smtp.socketFactory.fallback":"false"]

   }
}

However, when trying to connect to my own server using the same configurations according to documentation https://goo.gl/TCkzHG and the configuration that I use on thunderbird:

grails {
    mail {
        host = "mail.modemdepot.com.mx"
        port = 587
        username = "foo@example.com"
        password = "xxxxxx"
        props = ["mail.smtp.starttls.enable":"true", "mail.smtp.auth":"true","mail.debug":"true"]

    }
}

I get the following error:
DEBUG: JavaMail version 1.5.1
DEBUG: successfully loaded resource: /META-INF/javamail.default.providers
DEBUG: Tables of loaded providers
DEBUG: Providers Listed By Class Name: {com.sun.mail.smtp.SMTPSSLTransport=javax.mail.Provider[TRANSPORT,smtps,com.sun.mail.smtp.SMTPSSLTransport,Oracle], com.sun.mail.smtp.SMTPTransport=javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle], com.sun.mail.imap.IMAPSSLStore=javax.mail.Provider[STORE,imaps,com.sun.mail.imap.IMAPSSLStore,Oracle], com.sun.mail.pop3.POP3SSLStore=javax.mail.Provider[STORE,pop3s,com.sun.mail.pop3.POP3SSLStore,Oracle], com.sun.mail.imap.IMAPStore=javax.mail.Provider[STORE,imap,com.sun.mail.imap.IMAPStore,Oracle], com.sun.mail.pop3.POP3Store=javax.mail.Provider[STORE,pop3,com.sun.mail.pop3.POP3Store,Oracle]}
DEBUG: Providers Listed By Protocol: {imaps=javax.mail.Provider[STORE,imaps,com.sun.mail.imap.IMAPSSLStore,Oracle], imap=javax.mail.Provider[STORE,imap,com.sun.mail.imap.IMAPStore,Oracle], smtps=javax.mail.Provider[TRANSPORT,smtps,com.sun.mail.smtp.SMTPSSLTransport,Oracle], pop3=javax.mail.Provider[STORE,pop3,com.sun.mail.pop3.POP3Store,Oracle], pop3s=javax.mail.Provider[STORE,pop3s,com.sun.mail.pop3.POP3SSLStore,Oracle], smtp=javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]}
DEBUG: successfully loaded resource: /META-INF/javamail.default.address.map
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: trying to connect to host "mail.modemdepot.com.mx", port 587, isSSL false
220 mail.modemdepot.com.mx ESMTP Postfix (Ubuntu)
DEBUG SMTP: connected to host "mail.modemdepot.com.mx", port: 587
EHLO Ricardo-Pc
250-mail.modemdepot.com.mx
250-PIPELINING
250-SIZE 36700160
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
DEBUG SMTP: Found extension "PIPELINING", arg ""
DEBUG SMTP: Found extension "SIZE", arg "36700160"
DEBUG SMTP: Found extension "ETRN", arg ""
DEBUG SMTP: Found extension "STARTTLS", arg ""
DEBUG SMTP: Found extension "ENHANCEDSTATUSCODES", arg ""
DEBUG SMTP: Found extension "8BITMIME", arg ""
DEBUG SMTP: Found extension "DSN", arg ""
STARTTLS
220 2.0.0 Ready to start TLS

Error |
unable to find valid certification path to requested target. Stacktrace follows:
Message: unable to find valid certification path to requested target

As far as I can tell, the application can connect to the server, but then something is missing.
Can you please help me out with this? I think it is a mail server error rather than the java application.