R – I can send an email from the Rails app, but not an SMS text through an email gateway

Be sure to use System.Net.Mail, not the deprecated System.Web.Mail. Doing SSL with System.Web.Mail is a gross mess of hacky extensions.

using System.Net;
using System.Net.Mail;

var fromAddress = new MailAddress("from@gmail.com", "From Name");
var toAddress = new MailAddress("to@example.com", "To Name");
const string fromPassword = "fromPassword";
const string subject = "Subject";
const string body = "Body";

var smtp = new SmtpClient
{
    Host = "smtp.gmail.com",
    Port = 587,
    EnableSsl = true,
    DeliveryMethod = SmtpDeliveryMethod.Network,
    UseDefaultCredentials = false,
    Credentials = new NetworkCredential(fromAddress.Address, fromPassword)
};
using (var message = new MailMessage(fromAddress, toAddress)
{
    Subject = subject,
    Body = body
})
{
    smtp.Send(message);
}

Additionally go to the Google Account > Security page and look at the Signing in to Google > 2-Step Verification setting.

• If it is enabled, then you have to generate a password allowing .NET to bypass the 2-Step Verification. To do this, click on Signing in to Google > App passwords, select app = Mail, and device = Windows Computer, and finally generate the password. Use the generated password in the fromPassword constant instead of your standard Gmail password.
• If it is disabled, then you have to turn on Less secure app access, which is not recommended! So better enable the 2-Step verification.

If your application is not so critical you can use email to sms. SO has some questions about email to sms. You can search them.

I would prefer an SMS gateway than using a personal mobile phone. You cannot send BULK sms using a mobile phone at the same time. Mobile phones send one sms at a time so its time consuming.

In India SMS gateways are cheaper (for bulk purchases) than mobile phones. You can choose a Sender ID which can contain alphabets and numbers. This is another advantage of bulk sms as it will look more professional.

The Sender ID facility is not available when you send sms using a mobiole phone. Name can be displayed only if the receiver has your number stored.

Anoter advantage is reports. Gateways usually have reports. You can generate customised report. Think about option for delivery report when you send sms through phone ;-)