basE91 is an advanced method for encoding binary data as ASCII characters. It is similar to UUencode or base64, but is more efficient. The overhead produced by basE91 depends on the input data. It amounts at most to 23% and can range down to 14%.
LightningPigeon is an e-mail client designed to be efficient and non-bloated. The primary aim being of an educational value to the developers and the secondary aim of providing a client which works at top efficiency.