You can create a custom property called AdditionalEmailSender or a name of your choice in azure B2C...
I will put here a snipped of my real blazor app that's uses sendgrid so you can use it as guidance...
using SendGrid;
using SendGrid.Helpers.Mail;
namespace MyProj.Classes
{
public class SendMail
{
public async Task SendPassCode(string code, string email) {
var apiKey = "The Key";
var client = new SendGridClient(apiKey);
var from = new EmailAddress("from@domain.com ", "Display Name");
var subject = "Your Pass Code";
var to = new EmailAddress(email); // put your email in a variable after you got the account details
var plainTextContent = $"Code:{code}";
var htmlContent = $"<strong>Code:</strong> {code}";
var msg = MailHelper.CreateSingleEmail(from, to, subject, plainTextContent, htmlContent);
var response = await client.SendEmailAsync(msg).ConfigureAwait(false);
}
}
}