Unique ID in POP3 protocol

RFC 1939 specification says:

“The unique-id of a message is an arbitrary server-determined string, […], which uniquely identifies a message within a maildrop and which persists across sessions.”

“The server should never reuse an unique-id in a given maildrop, for as long as the entity using the unique-id exists.”

So in theory if the email is deleted server may reuse the same unique-id.

“While it is generally preferable for server implementations to store arbitrarily assigned unique-ids in the maildrop, this specification is intended to permit unique-ids to be calculated as a hash of the message.

Clients should be able to handle a situation where two identical copies of a message in a maildrop have the same unique-id.”

Mail.dll will not throw exception in such case, but please note, that internally Mail.dll uses dictionaries to store unique-ids and Pop3.GetAll() method will not return duplicates.

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