Base64 is a binary-to-text encoding scheme that converts binary data into ASCII characters. In email systems, Base64 encoding allows attachments, images, and non-ASCII text to be transmitted safely through protocols that only support text-based content.
Email protocols like SMTP were originally designed to handle only 7-bit ASCII text. Base64 encoding bridges this limitation by allowing binary content such as images, PDFs, and other attachments to be embedded in email messages. Without Base64, email attachments would be corrupted during transmission. Understanding Base64 helps troubleshoot encoding issues, optimize email size, and ensure attachments reach recipients intact.
Base64 encoding works by taking binary data and dividing it into 6-bit groups, then mapping each group to one of 64 printable ASCII characters (A-Z, a-z, 0-9, +, /). This process increases the data size by approximately 33%, but ensures the content can pass through text-only email systems without corruption. When an email with attachments is sent, the MIME standard uses Base64 to encode binary files into text that email servers can safely transmit.
Base64 encoding converts 3 bytes of binary data into 4 ASCII characters. This 4:3 ratio results in approximately 33% size increase. Additionally, line breaks may be added every 76 characters per MIME specification, adding slightly more overhead.
For small icons and logos under 10KB, Base64 embedding can improve load reliability. For larger images, external links are better since they reduce email size, allow caching, and provide tracking capabilities. Most email best practices recommend limiting inline Base64 images.
Large Base64-encoded content can trigger spam filters if it makes emails exceed size limits or creates suspicious patterns. Some email clients may also block or strip large Base64 attachments. Keeping total email size under 100KB helps maintain good deliverability.
Base64 is better for binary data and non-text content, encoding everything uniformly. Quoted-printable is more efficient for text with occasional special characters, as it only encodes non-ASCII bytes. Email clients choose the appropriate encoding based on content type.
Start using EmailVerify today. Verify emails with 99.9% accuracy.