How to make the image size adjustable to mail size

There are a few ways to make an image size adjustable to the mail size, depending on the platform or tool you're using. Here are a few approaches:

1. Use a responsive image

If you're using a content management system (CMS) like WordPress, you can use a responsive image plugin like wp-responsive-image or responsive-image to automatically resize images based on the screen size or mail size.

2. Use CSS media queries

You can use CSS media queries to define different image sizes for different screen sizes or mail sizes. For example:

/* For small screens (e.g. mobile) */
@media only screen and (max-width: 480px) {
  img {
    width: 100%;
    height: auto;
  }
}

/* For medium screens (e.g. tablet) */
@media only screen and (min-width: 481px) and (max-width: 768px) {
  img {
    width: 75%;
    height: auto;
  }
}

/* For large screens (e.g. desktop) */
@media only screen and (min-width: 769px) {
  img {
    width: 50%;
    height: auto;
  }
}

3. Use a library like Masonry

Masonry is a JavaScript library that allows you to create responsive grids of images. You can use it to create a grid of images that automatically adjusts to the mail size.

4. Use a server-side language like PHP

If you're using a server-side language like PHP, you can use a library like image_resize to resize images based on the mail size.

5. Use a mail client's built-in image resizing

Some mail clients, like Gmail, have built-in image resizing features that can automatically resize images to fit the mail size.

Here's an example of how you can use PHP to resize an image based on the mail size:

<?php
  // Get the mail size
  $mail_size = get_mail_size();

  // Set the image dimensions
  $image_width = 800;
  $image_height = 600;

  // Resize the image
  $image = imagecreatefromjpeg('image.jpg');
  $new_width = $image_width * ($mail_size / 1024);
  $new_height = $image_height * ($mail_size / 1024);
  $image = imagecopyresized($image, $new_width, $new_height);

  // Output the resized image
  header('Content-Type: image/jpeg');
  imagejpeg($image);
?>

Note that this is just a basic example, and you may need to adjust the code to fit your specific use case.