Since Synology Web Station released. PHP function had been combine in Web Station GUI. The problem is the configuration of the ssmtp application, which is broken for now. I have no idea if Synology will fix it or not.
To make smtp via php work properly. You should 1.Install the Synology Mail Server application.
Note:If you want to use an external mail server (as I do), you MUST set it up as an SMTP relay.
This is what I have done, since I run my own mail server on a different box. I assume you can also set it up to relay through other email services such as Gmail .
2.Once you have set up Mail Server, make the following changes from a command prompt session, open php.ini file with Web station GUI.
sendmail_from = youremail@yourprovider
sendmail_path = /var/packages/MailServer/target/sbin/sendmail -t
3.After restarting Apache the ini-file gets loaded, and PHP can send mails again.
To access terminal via ssh: ssh username@serveraddress (remember to enable 22 port for ssh)
synoservicectl –restart httpd-user