As the world’s largest encrypted email provider, working with IMAP (Internet Message Access Protocol) is something that we do on a daily basis. IMAP is core to the Proton Mail Bridge app, which lets you add Proton Mail encryption to standard email clients, such as Outlook, Thunderbird, or Apple Mail.
But IMAP goes beyond Proton Mail. It is one of two standard email retrieval protocols (the other being POP) that nearly every email app uses to access and manage your emails. So, in essence, it powers email globally.
Today, we’re introducing Gluon(new window), a new IMAP library written in the Go programming language designed to be high-performance, reliable, developer-friendly, and, most importantly, open-source.
Together with the launch of Gluon, we are also releasing a new version of the Proton Mail Bridge that is powered by Gluon. As a result of the innovations below, the new Proton Mail Bridge is 1000% faster, far more reliable, and also compatible with more email clients.
Why create a new IMAP library?
Email needs to be reliable, but it also needs to be high-performance, particularly as the typical inbox size has grown significantly over the past decade. Many open-source IMAP implementations tend to optimize for one and not the other, leading to pretty significant trade-offs or bugs.
Gluon seeks to bridge that gap and overcome the limitations in existing open-source IMAP libraries, which are often poorly maintained, or not entirely scalable. Gluon does this by utilizing an architecture that relies upon a “snapshot” system.
IMAP clients typically refer to messages by their “sequence number”, the message’s position in a mailbox. The first message has the sequence number “1”, the second “2”, and so on. If a client wants to mark a message as “read”, it will send a command to the server such as “mark message 5 as read”. But what if another client deleted the fourth message in the mailbox? The sequence numbers of all messages after the deleted message will be shifted down by one; the client that sent the “mark message 5 as read” command now refers to a different message than it intended.
IMAP servers (which include applications such as the Proton Mail Bridge) need to be able to handle this situation. When one client moves messages into or out of a mailbox, the server needs to notify all other clients of the changes so that they can update their own view of the mailbox. And until the clients have received the update, the server needs to remember what each client thinks the mailbox looks like to correctly interpret the client’s comman
