Error with HTML form inserted in CMS page

[crespil]

Hello everyone. I have an HTML form that I need to display (and execute) within a CMS page. The form looks Ok, but after clicking "SEND" it gives me the following error:

Warning: mail(/var/sendmail/phpmail.log): failed to open stream: Permission denied in /www/mysite/htdocs/modules/formularios/correo.php on line 28

I put my form files in a folder with permissions 755 and 644 for the files. I understand this is common, but I can't get it to work. Please, if anyone has advice on how to solve this, it would be appreciated...

Thanks in advance