A few notes for you to consider

SMTP usually requires authentication (login/password), so that would need to be set up. Additionally, you would need to ensure you're using the correct port. For example, Gmail, Yahoo! and many others require port 465 with SSL encryption. Some might require StartTLS on port 587.

As for determining the SMTP server automatically, I don't know of any way to do it. One might use smtp.<domain> while another might use mail.<domain>, where <domain> is something like comcast.net or gmail.com. Some might have a server named smtp-878C13B1.<domain> as one of many SMTP servers, none of which are smtp.<domain> or mail.<domain>. Others might simply use <domain> and if traffic is trying to connect to port 25 or 465 or 587, it would route that traffic to an SMTP server.

Alternatively, you might be able to use an installed program such as Microsoft Outlook or Windows Mail if it is already set up properly. This is probably easier than handling everything yourself, unless of course you choose to allow the input of the SMTP server address and port number as well as login credentials where necessary and the proper encryption settings. The address could be a numeric IP address (don't forget that IPv6 exists!) or a domain name such as smtp.comcast.net.