Architecture
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These descriptions are out of date. Raw messages are stored in MongoDB GridFS instead of LevelDB
Messages are dropped for delivery either by SMTP or HTTP API. Message is processed as a stream, so it shouldn't matter if the message is very large in size (except if a very large message is submitted using the JSON API). This applies also to DKIM body hash calculation – the hash is calculated chunk by chunk as the message stream flows through (actual signature is generated out of the body hash when delivering the message to destination). The incoming stream starts from incoming connection and ends in LevelDB, so if there's an error in any step between these two, the error is reported back to the client and the message is rejected. If impartial data is stored to LevelDB it gets garbage collected after some time (all message bodies without referencing delivery rows are deleted automatically)
Delivering messages to destination
