Generating Excel files in C# is a common task for developers building reporting systems, exporting structured data, or automating Excel-based workflows. Whether you're building desktop tools, web APIs with ASP.NET Core, or cross-platform apps using .NET, the ability to generate .xlsx files programmatically can simplify many data exchange scenarios.

In this guide, you'll learn how to generate Excel files in C# using Spire.XLS for .NET — a standalone Excel library that works seamlessly across different types of .NET applications — from desktop tools to web services and background jobs. We’ll cover use cases such as creating spreadsheets from scratch, exporting data from a DataTable, generating files on the server side, and applying formatting or formulas, all with practical code examples.

Table of Contents

• Set Up the Environment
• Create Excel Files from Scratch in C#
• Export DataTable to Excel in C#
• Apply Formatting and Formulas in Excel
• Generate Excel Files in ASP.NET Core
• Generate Excel Files in ASP.NET Web Forms
• FAQ
• Conclusion

Set Up the Environment

Spire.XLS for .NET is a lightweight Excel library that allows you to create .xlsx/.xls files entirely through code — without installing Microsoft Office or using COM Interop. This makes it an ideal solution for web servers, microservices, and cloud-hosted applications.

You can install the library via NuGet:

Install-Package Spire.XLS

For smaller tasks, Free Spire.XLS for .NET is also a good choice:

Install-Package FreeSpire.XLS

Create Excel Files from Scratch in C#

For simple tasks like configuration files, small datasets, or template generation, creating an Excel file from scratch in C# provides full control over content and layout.

The example below shows how to generate a basic worksheet with text and numeric data:

using Spire.Xls;

// Create a new workbook and worksheet
Workbook workbook = new Workbook();
Worksheet sheet = workbook.Worksheets[0];
sheet.Name = "Summary";

// Fill in headers and data
// Access cells by name
sheet.Range["A1"].Text = "Employee";
sheet.Range["B1"].Text = "Department";
sheet.Range["C1"].Text = "Salary";

// Access cells by row and column
sheet.Range[2, 1].Text = "Alice";
sheet.Range[2, 2].Text = "HR";
sheet.Range[2, 3].NumberValue = 6500;

sheet.Range[3, 1].Text = "Bob";
sheet.Range[3, 2].Text = "IT";
sheet.Range[3, 3].NumberValue = 7200;

// Apply styles
CellStyle headerStyle = workbook.Styles.Add("Header");
headerStyle.Font.IsBold = true;
sheet.Range["A1:C1"].Style = headerStyle;
// sheet.Range[1, 1, 1, 3].Style = headerStyle;

// Auto-fit columns
sheet.AllocatedRange.AutoFitColumns();

// Save the file
workbook.SaveToFile("BasicExcel.xlsx", ExcelVersion.Version2016);
workbook.Dispose();

Example output: A basic Excel file with employee names, departments, and salaries created in C#.

This approach works entirely without Excel installed, and is ideal for lightweight, structured exports.

Export DataTable to Excel in C#

When working with databases or APIs, exporting a DataTable directly to Excel in C# is often necessary. Instead of looping through rows manually, Spire.XLS provides an efficient way to load structured data in one line.

Here’s how you can convert a DataTable into a worksheet, including headers:

using System.Data;
using Spire.Xls;

// Create a simulated data table
DataTable dt = new DataTable("Products");
dt.Columns.Add("Product Name", typeof(string));
dt.Columns.Add("Price", typeof(double));
dt.Columns.Add("Stock", typeof(int));

dt.Rows.Add("Laptop", 1299.99, 20);
dt.Rows.Add("Monitor", 199.5, 50);
dt.Rows.Add("Mouse", 25.75, 150);

// Import into Excel
Workbook workbook = new Workbook();
Worksheet sheet = workbook.Worksheets[0];
sheet.Name = "Inventory";
sheet.InsertDataTable(dt, true, 1, 1);

// Auto-fit column widths
sheet.AllocatedRange.AutoFitColumns();

// Save the file
workbook.SaveToFile("InventoryReport.xlsx", ExcelVersion.Version2016);
workbook.Dispose();

Example output: Excel spreadsheet generated from a DataTable containing product details, prices, and stock levels.

This is a common approach for exporting reports, inventory lists, and analytics — with no Excel or Interop automation required.

Related article: Convert Data Between Excel Files and DataTable in C#

Apply Formatting and Formulas in Excel Using C#

In addition to exporting raw data, you can generate professional Excel files in C# by applying formatting, styling, and formulas — improving readability and enabling automatic calculations.

Below is an example that demonstrates basic styling and formula use:

using Spire.Xls;
using System.Drawing;

Workbook workbook = new Workbook();
Worksheet sheet = workbook.Worksheets[0];
sheet.Name = "Sales Report";

// Set header labels
sheet.Range["A1"].Text = "Item";
sheet.Range["B1"].Text = "Price";
sheet.Range["C1"].Text = "Quantity";
sheet.Range["D1"].Text = "Total";

// Add sample data
string[,] items = {
    { "Pen", "1.5", "10" },
    { "Notebook", "3.75", "5" },
    { "Eraser", "0.99", "20" }
};

for (int i = 0; i < items.GetLength(0); i++)
{
    int row = i + 2;
    sheet.Range[$"A{row}"].Text = items[i, 0];
    sheet.Range[$"B{row}"].NumberValue = double.Parse(items[i, 1]);
    sheet.Range[$"C{row}"].NumberValue = double.Parse(items[i, 2]);
    sheet.Range[$"D{row}"].Formula = $"=B{row}*C{row}";
}

// Style: Header row
CellStyle headerStyle = workbook.Styles.Add("HeaderStyle");
headerStyle.Font.IsBold = true;
headerStyle.Font.Color = Color.White;
headerStyle.Font.Size = 12;
headerStyle.KnownColor = ExcelColors.DarkBlue;
headerStyle.HorizontalAlignment = HorizontalAlignType.Center;
headerStyle.VerticalAlignment = VerticalAlignType.Center;
headerStyle.Borders[BordersLineType.EdgeTop].LineStyle = LineStyleType.Thick;
headerStyle.Borders[BordersLineType.EdgeLeft].LineStyle = LineStyleType.Thick;
sheet.Range["A1:D1"].Style = headerStyle;
sheet.Range["A1:D1"].RowHeight = 22;

// Style: Data cells
CellStyle dataStyle = workbook.Styles.Add("DataStyle");
dataStyle.NumberFormat = "\"$\"#,##0.00";
dataStyle.HorizontalAlignment = HorizontalAlignType.Right;
dataStyle.VerticalAlignment = VerticalAlignType.Center;
dataStyle.Borders[BordersLineType.EdgeLeft].LineStyle = LineStyleType.Thin;
dataStyle.Borders[BordersLineType.EdgeBottom].LineStyle = LineStyleType.Thin;

// Apply data style to Price, Quantity, Total
sheet.Range["B2:D4"].Style = dataStyle;

// Optional: Alternating row colors for readability
for (int r = 2; r <= 4; r++)
{
    if (r % 2 == 0)
        sheet.Range[$"A{r}:D{r}"].Style.KnownColor = ExcelColors.LightYellow;
}

// Adjust widths and heights
sheet.AllocatedRange.AutoFitColumns();
sheet.AllocatedRange.RowHeight = 20;

// Save file
workbook.SaveToFile("styled.xlsx", FileFormat.Version2016);
workbook.Dispose();

Example output: A styled Excel sheet with headers, formulas, alternating row colors, and formatted currency values.

By using C# and Spire.XLS, you can apply styles, borders, colors, alignments, and Excel-compatible formulas to generate clean, automated, and user-friendly Excel reports.

To further enhance your Excel reports, you can also apply number formats such as currency, percentage, or custom formats. Learn more about setting number formats in C#

Generate Excel Files in ASP.NET Core

In modern ASP.NET Core applications (e.g., .NET 6/7/8), generating Excel files is a common requirement for admin dashboards, data exports, and reporting features. The example below shows how to generate an Excel file on the server and return it as a downloadable file from a Razor Page handler.

Here’s how you can implement it in a Razor Pages project:

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Spire.Xls;
using System.Data;

public class ExportModel : PageModel
{
    public IActionResult OnGet()
    {
        // Simulated data
        DataTable dt = new DataTable("Sales");
        dt.Columns.Add("Date", typeof(DateTime));
        dt.Columns.Add("Product", typeof(string));
        dt.Columns.Add("Revenue", typeof(double));

        dt.Rows.Add(DateTime.Today.AddDays(-2), "Laptop", 1250.00);
        dt.Rows.Add(DateTime.Today.AddDays(-1), "Monitor", 320.50);
        dt.Rows.Add(DateTime.Today, "Mouse", 25.99);

        // Create Excel workbook and sheet
        Workbook workbook = new Workbook();
        Worksheet sheet = workbook.Worksheets[0];
        sheet.Name = "DailySales";

        // Insert data
        sheet.InsertDataTable(dt, true, 1, 1);

        // Apply simple header style
        CellStyle headerStyle = workbook.Styles.Add("HeaderStyle");
        headerStyle.Font.IsBold = true;
        sheet.Rows[0].Style = headerStyle;
        sheet.AllocatedRange.AutoFitColumns();

        // Save to memory stream
        using var stream = new MemoryStream();
        workbook.SaveToStream(stream, FileFormat.Version2016);
        stream.Position = 0;

        // Return file to browser
        return File(stream.ToArray(),
            "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
            "SalesReport.xlsx");
    }
}

Example output: Daily sales report generated in a .NET 8 console app with date, product, and revenue columns.

This method is ideal for web-based reporting tools, internal portals, and admin dashboards that require dynamic Excel downloads.

• ✅ Works in ASP.NET Core 3.1, .NET 5, .NET 6, .NET 7, .NET 8
• ✅ Suitable for: Razor Pages, MVC, and API endpoints with file download support

Generate Excel Files in ASP.NET Web Forms

If you're building an internal admin panel or classic ASP.NET Web Forms application, you may want to allow users to download Excel files directly from the browser. The example below demonstrates how to create an Excel file entirely in memory and return it in the HTTP response for immediate download — without saving it to disk.

using Spire.Xls;
using System;
using System.IO;

namespace YourNamespace
{
    public partial class Default : System.Web.UI.Page
    {
        protected void btnExport_Click(object sender, EventArgs e)
        {
            // Create Excel file and output for download
            Workbook workbook = new Workbook();
            Worksheet sheet = workbook.Worksheets[0];
            sheet.Name = "Users";

            // Headers
            string[] headers = { "ID", "Name", "Department", "Join Date" };
            for (int i = 0; i < headers.Length; i++)
            {
                sheet.Range[1, i + 1].Text = headers[i];
                sheet.Range[1, i + 1].Style.Font.IsBold = true;
            }

            // Sample data
            string[,] data = {
                { "U001", "Gemma", "HR", "2023-01-15" },
                { "U002", "Bill", "IT", "2022-11-03" }
            };

            // Fill data
            for (int r = 0; r < data.GetLength(0); r++)
                for (int c = 0; c < data.GetLength(1); c++)
                    sheet.Range[r + 2, c + 1].Text = data[r, c];

            // Auto-fit column widths
            sheet.AllocatedRange.AutoFitColumns();

            // Export for browser download
            using (MemoryStream ms = new MemoryStream())
            {
                workbook.SaveToStream(ms, FileFormat.Version2016);
                byte[] bytes = ms.ToArray();
                Response.Clear();
                Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                Response.AddHeader("Content-Disposition", "attachment; filename=Users.xlsx");
                Response.BinaryWrite(bytes);
                Response.End();
            }
        }
    }
}

Example output: Excel file created and streamed to browser in ASP.NET containing employee records.

This pattern allows Excel files to be generated and downloaded dynamically, without writing to disk or requiring Office installed on the server.

FAQ

How to create an Excel file from C#?

You can use a library like Spire.XLS to create a new workbook, write data to worksheets, and save it as an Excel file — all without Office installed.

How to export an Excel file in C#?

If you want to export data (e.g. from a DataTable), you can load it into a worksheet and save the file using Spire.XLS. It supports automatic column headers and formatting.

How to generate Excel files in ASP.NET using C#?

You can generate Excel files in both ASP.NET Web Forms and ASP.NET Core using Spire.XLS. In ASP.NET Core, create the file in memory and return it in the HTTP response. In Web Forms, use a similar approach with Response.BinaryWrite() to stream the file to the browser.

Is Spire.XLS compatible with .NET Core?

Yes. It supports .NET Core 3.1+, .NET 5, .NET 6, .NET 7, and .NET 8, making it suitable for cross-platform Excel generation.

Conclusion

With Spire.XLS for .NET, you can easily generate Excel files in C# for any scenario — including desktop, ASP.NET Core, and classic Web Forms applications. Whether you need to export a DataTable, generate formatted reports, or automate Excel output, this guide helps you build Excel files in C# with zero dependencies.

Apply for a Free Temporary License to unlock all features and remove evaluation warnings.

Sending emails from a C# application is a common task in business and enterprise development. Whether you're delivering a project update, sending alerts, or automating reporting workflows, reliable email functionality is essential.

In this article, we’ll walk through how to send emails in C# using Spire.Email for .NET, a powerful component that simplifies SMTP communication and email formatting. We'll explore SMTP configuration, Gmail integration, HTML and plain-text content, file attachments, and multiple recipients.

Table of Contents

• 1. Project Setup
• 2. Send a Plain-Text Email via SMTP
• 3. Send HTML Email with Attachments via Gmail SMTP
• 4. Advanced Email Features with Spire.Email
• 5. Common Errors and Troubleshooting
• 6. Use Cases for Spire.Email
• 7. Free License
• 8. FAQ

1. Project Setup

To begin, create a .NET project (Console App or ASP.NET) and add the Spire.Email for .NET package.

Install via NuGet:

Install-Package Spire.Email

Or manually download the Spire.Email package and reference the Spire.Email.dll from your local installation package.

2. Send a Basic Email via SMTP in C#

The example below shows how to use Spire.Email to send a plain-text email through an SMTP server.

using Spire.Email;
using Spire.Email.Smtp;

// Configure the SMTP client
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtp.example.com";
smtp.Port = 587;
smtp.Username = "your@example.com";
smtp.Password = "your_password";
smtp.ConnectionProtocols = ConnectionProtocols.StartTls;

// Create maill addresses
MailAddress sender = new MailAddress("your@example.com", "Sender Name");
MailAddress recipient = new MailAddress("recipient@example.com", "Recipient Name");
MailMessage message = new MailMessage(sender, recipient);

// Set the email content
message.Subject = "Test Email";
message.BodyText = "This is a plain-text test email.";

// Send the email
smtp.SendOne(message);

Explanation:

• Uses MailAddress and MailMessage from Spire.Email
• Establishes a secure SMTP connection using ConnectionProtocols.StartTls

The screenshot below shows the actual email received using the above SMTP code.

3. Send HTML Email with Attachments via Gmail SMTP in C#

The following C# code example demonstrates how to send an HTML-formatted email using Gmail SMTP, including multiple recipients, a file attachment, and plain-text fallback for clients that do not support HTML.

using Spire.Email;
using Spire.Email.Smtp;

// Create MailAddress objects
MailAddress from = new MailAddress("your@gmail.com", "Your Name");
MailAddress to1 = new MailAddress("user1@example.com", "User One");
MailAddress to2 = new MailAddress("user2@example.com", "User Two");

// Create a mail message
MailMessage message = new MailMessage(from, to1);
message.To.Add(to2);
message.Cc.Add(new MailAddress("cc@example.com", "CC Person"));
message.Bcc.Add(new MailAddress("bcc@example.com"));

// Set the body HTML and text for the message
message.Subject = "Monthly Report - June 2025";
message.BodyHtml = "<h2 style='color:#2E86C1;'>Report Summary</h2><p>Please see the attached PDF report.</p>";
message.BodyText = "Report Summary - please see the attached PDF.";

// Add an attachment to the email
Attachment attachment = new Attachment(@"Sample.pdf");
message.Attachments.Add(attachment);

// Configure the SMTP client
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtp.gmail.com";
smtp.Port = 587;
smtp.Username = "your@gmail.com";
smtp.Password = "your_app_password";
smtp.ConnectionProtocols = ConnectionProtocols.StartTls;

// Sen the email
smtp.SendOne(message);

Explanation:

• Uses MailAddress, MailMessage, Attachment, and SmtpClient from Spire.Email
• Combines BodyHtml and BodyText to support HTML and plain-text email clients
• Adds multiple recipients via To.Add(), Cc.Add(), and Bcc.Add()
• Sends email securely through Gmail using ConnectionProtocols.StartTls

Gmail requires App Passwords if 2FA is enabled.

The following screenshot shows the HTML-formatted email with rich text, CC and BCC recipients, and a PDF attachment, as received from Gmail SMTP.

Related article: How to Send an Email with Attachments in C#

4. Advanced Email Features with Spire.Email

This section demonstrates advanced C# email-sending capabilities using Spire.Email, including embedded images and batch dispatch.

// Prepare an email with embedded image
MailMessage message = new MailMessage(
    new MailAddress("your@domain.com", "Sender"),
    new MailAddress("client@domain.com", "Client"));

message.Subject = "Branding Update";
message.BodyHtml = "<h1>Our New Logo</h1><img src=\"cid:logo\">";
message.BodyText = "Please view this message in HTML to see the image.";

Attachment logo = new Attachment(@"C:\Images\logo.png");
logo.ContentId = "logo";
logo.DispositionType = "Inline";
message.Attachments.Add(logo);

// Prepare a second email
MailMessage message2 = new MailMessage(
    new MailAddress("your@domain.com"),
    new MailAddress("sales@domain.com"));
message2.Subject = "Weekly Summary";
message2.BodyText = "This is an automated weekly update.";

// Create SMTP client
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtp.domain.com";
smtp.Port = 587;
smtp.Username = "your@domain.com";
smtp.Password = "your_password";
smtp.ConnectionProtocols = ConnectionProtocols.StartTls;

// Send one email
smtp.SendOne(message);

// Send emails in batch
smtp.SendSome(new List<MailMessage> { message, message2 });

Explanation:

• Attachment.ContentId and DispositionType = "Inline" allow inline images using CID references in HTML.
• SendOne() sends a single message.
• SendSome() sends multiple messages as a batch. Ideal for scheduled reports or group notifications.

The following screenshot shows an email with an embedded company logo and a plain-text fallback, demonstrating how Spire.Email renders HTML content with inline images.

You may also like: Creating MSG Files with RTF Body and Attachments Using C#

5. Common Errors and Troubleshooting

6. Use Cases for Spire.Email

Spire.Email for .NET is suitable for:

• Daily/weekly automated reporting
• User signup and notification emails
• Order confirmations with attachments
• Form submission alerts
• Embedded-image newsletters

Its clean API removes the need to manually handle SMTP headers, MIME formatting, and encoding issues.

Conclusion

With Spire.Email for .NET, developers can quickly build robust and flexible email-sending features directly into C# applications. Whether the goal is to deliver transactional messages, generate styled reports, or dispatch scheduled newsletters, this component provides a clean, reliable API that simplifies every step of the process.

By supporting plain-text and HTML formats, attachments, Gmail SMTP, embedded images, and batch sending, Spire.Email helps streamline email integration without the overhead of external dependencies.

7. Apply for a Free Temporary License

To remove the evaluation warning in the email body or attachment footer, you can apply for a free temporary license:

Request a Free 1-Month License

Simply fill out the form and follow the instructions to apply the license in your project. This enables full feature access during evaluation.

8. FAQ

How to send HTML email in C#?

You can set the BodyHtml property of the MailMessage object to send an HTML email using Spire.Email. You can also include BodyText as a fallback for clients that don't support HTML.

How to send email to multiple recipients in C#?

Add multiple recipients using message.To.Add(), message.Cc.Add(), and message.Bcc.Add() methods. Spire.Email supports To, Cc, and Bcc fields.

How to use SMTP to send email in ASP.NET or MVC projects?

The SMTP usage in ASP.NET or MVC is the same as in Console applications. Simply configure the SmtpClient with host, port, credentials, and use the same SendOne() or SendSome() methods to dispatch your message.