Base64 converts binary files into text so they can travel through email safely. Learn how Base64 affects email size and deliverability.
Base64 is an encoding method that converts binary data into text characters. Email systems were originally designed for text, so attachments and some embedded content are often encoded with Base64 to transmit reliably.
The practical downside is size overhead: Base64 typically increases the data size by roughly one-third, which can push messages over common provider limits. This matters when you include large PDFs, images, or multiple attachments.
If email size becomes an issue, switch to hosted links, compress files, or reduce image weight. Keeping messages small improves load time and reduces the chance of filtering or delivery problems.