Pass Login Credentials Via URL String?

I own a website, and the hosting company has set-up Smarter Mail Enterprises 5.5 as the email provider. I want to allow my visitors to sign into their pre-configured email addresses right from the home page of my website, rather than going to webmail.domainname.com, so I am wondering if there is a way that I can have them enter their email address (which is their user id) and their password on my site, and if I can pass that information via the url string to log them in automatically. Does anyone know if this is possible, and if so, can you point me in the right direction? I am a fairly new coder.

 

Thank you so much!