Gluon, a high-performance IMAP library
&gt; 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.<p>&gt; 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 commands.<p>Holy F what a clusterfuck