using var connection = new MySqlConnection("Server=YOURSERVER;User ID=YOURUSERID;Password=YOURPASSWORD;Database=YOURDATABASE");

await connection.OpenAsync();

using var command = new MySqlCommand("SELECT mail, recipient FROM table;", connection);
using var reader = await command.ExecuteReaderAsync();
while (await reader.ReadAsync())
{
	var mail = reader.GetString("mail");
	var recipient = reader.GetString("recipient");

	label.Text.Expression = $"Hello, {recipient}";

	var pdf = pdfExporter.ExportForm(form);

	var mailMessage = new MailMessage
	{
		From = new MailAddress("Адрес электронной почты защищен от спам-ботов. Для просмотра адреса в браузере должен быть включен Javascript."),
		Subject = "subject",
		Body = "<h1>Hello</h1>",
		IsBodyHtml = true,
	};
	mailMessage.To.Add(mail);

	var attachment = new Attachment(new MemoryStream(pdf), MediaTypeNames.Application.Pdf);
	mailMessage.Attachments.Add(attachment);

	smtpClient.Send(mailMessage);
}