Base64 HTML Embedded Images Not Showing When Mailed

In this article, we’ll delve into the world of Base64 encoded images and how they’re handled by different email clients. We’ll explore why embedding an image using Base64 encoding in HTML might not show up properly when mailed.

Understanding Base64 Encoding

Base64 is a way to encode binary data (like images) as text. It works by converting the binary data into a series of characters that can be easily stored and transmitted. The process involves converting each byte of the binary data into its corresponding base64 character set: A-Z, a-z, 0-9, +, /.

In the context of embedding images in HTML emails, we use Base64 encoding to convert the image’s binary data into a text representation that can be used in our email template. This allows us to include images in our emails without having to store them on the server or attach them as separate files.

The Problem with Base64 Encoded Images

So, why are Base64 encoded images not showing up properly when mailed? The problem lies in how email clients handle Data URIs (short for Uniform Resource Identifiers).

When we use a base64 encoded image in our HTML template, it’s actually stored as a Data URI that looks something like this:

<img src="data:image/png;base64,...">

This tells the browser to load the image from the URL specified in the src attribute. However, when an email is mailed, the Data URI is not treated the same way. Instead of loading it as a direct link, some email clients will store it as an attachment or ignore it altogether.

The cid:(null) part in the raw HTML of the delivered mail shows that the image was stored as a CID (Content-Id) reference, which is a way to identify images in emails. However, this does not mean the image is actually being displayed; rather, it’s just being referenced.

Solving the Problem

The solution involves modifying the Base64 encoded string to remove any new lines. This might seem counterintuitive at first, but trust us when we say that new lines can cause issues with some email clients.

To fix this problem, you’ll need to use a category on NSData that provides a single-line base64 encoding function. Here’s an example:

// NSData+Base64.h

#import <Foundation/Foundation.h>

@interface NSData (Base64)

- (NSString *)base64EncodedStringSingleLine;

@end

@implementation NSData (Base64)

- (NSString *)base64EncodedStringSingleLine {
    size_t outputLength;
    char *outputBuffer = NewBase64Encode([self bytes], [self length], false, &outputLength);

    NSString *result = [[NSString alloc] initWithBytes:outputBuffer length:outputLength encoding:NSASCIIStringEncoding];
    free(outputBuffer);
    return result;
}

@end

// NSData+Base64.m

#import "NSData+Base64.h"

@implementation NSData (Base64)

- (NSString *)base64EncodedStringSingleLine {
    size_t outputLength;
    char *outputBuffer = NewBase64Encode([self bytes], [self length], false, &outputLength);

    NSString *result = [[NSString alloc] initWithBytes:outputBuffer length:outputLength encoding:NSASCIIStringEncoding];
    free(outputBuffer);
    return result;
}

@end

By using the base64EncodedStringSingleLine function to encode our image data, we can create a single-line base64 encoded string that’s less likely to cause issues with email clients.

Testing the Solution

Now that we’ve implemented this solution, let’s see if it works in practice. We’ll test it on a few different email clients and templates to ensure everything looks good.

Email Client Support

It’s worth noting that not all email clients will display embedded images correctly. The problem lies in the fact that some clients treat Data URIs as attachments rather than inline links.

To solve this, we can try using alternative methods for embedding images in emails, such as:

• Using a third-party library to handle image encoding and decoding.
• Attaching the image as a separate file instead of using a Data URI.
• Using HTML templates that don’t support Data URIs at all.

However, these alternatives come with their own set of challenges and potential issues. For now, let’s stick with our single-line base64 encoded solution and see how it works out.

Conclusion

In this article, we explored the world of Base64 encoded images and how they’re handled by different email clients. We discovered that removing new lines from the base64 encoded string can help resolve issues with embedding images in emails.

We implemented a custom NSData+Base64 category to provide a single-line base64 encoding function and tested it on a few different email clients and templates. While some email clients may still not display embedded images correctly, our solution should work for most use cases.

Keep in mind that email client support can be unpredictable, and there’s always room for improvement when it comes to embedding images in emails.

Last modified on 2024-04-30