I have recently encounter a problem Error 500 with running SEF on a joomla website. I was stumbled because all SMTP configuration in the Joomla (Site -> General Configurations ->Server) where correct. Here are the steps that took me fix Error 500 and to make my Contact Us from working with SEF. Contact Us Error 500 Troubleshooting First.
Go to (Site -> General Configurations ->Server)
1. Make sure that Mail Settings are correct
(Mailer, Mail from, Sendmail Path, SMTP Authentication)
2. Go to Site Tab
Set all settings under SEO Settings to NO
3. Go to you website and try to submit a form to see if it works with out SEF (SEO Links)
If it works then go to step 4 if the contact form is not working and you get Error go to step 1 and make sure all your email configuration are correct.
4. If the Contact Us Form Works and you don’t get Error 500
Then the issue could be in your template not in Contact form or SEF Extension.
You have to download from your website following file default_from.php the file is located in
templates/YOUR-TEMPLATE-NAME/html/com_contact/contact/default_form.php
5. Edit the default_from.php
a. Find <input type=”hidden” name=”view” value=”contact” />
b. Add before the line a <input type=”hidden” name=”option” value=”com_contact” />
If your default_from.php file had line b missing then the Error 500 issue will be resolved once you save the file and upload back to your server.
6. Go to Site -> General Configurations ->Site
Set all settings under SEO Settings to Yes
Now if you submit your Contact From on your website with SEO setting enabled your form should work, and you would not get Error 500.