Skip to main content

UID

property UID: String read write;

Example​

procedure LogMailboxIdentity;
var
  Msg: TIdMessage;
begin
  Msg := Email;
  if Msg = nil then Exit;

  if Msg.UID <> '' then
    Log('Fetched IMAP UID: ' + Msg.UID);
end;

Usage​

UID stores the IMAP server's mailbox-scoped unique identifier as an unvalidated String separate from Message-ID and serialized content.

Additional Technical Info​

UID stores an IMAP unique identifier associated with a message in a selected mailbox. It is not the Internet message MsgId: the same message copied to another mailbox can have a different UID, while Message-ID normally remains part of the message content.

The property is a direct String field. Its setter performs no numeric, range, mailbox or UIDVALIDITY check. Empty means no UID is currently recorded. New and cleared messages have an empty value because ClearHeader resets it.

How it is populated and used​

Indy's IMAP fetch/retrieve paths parse the server's UID response token and assign it to this property, often at the same time as Flags. Some UID-based retrieve paths fall back to the caller-supplied UID when the response omits it. Server code also uses UID to locate a mailbox collection item and can construct a temporary TIdMessage containing only UID for deletion rollback.

Assigning UID yourself only changes the in-memory object. It does not allocate a server UID, move the message, issue an IMAP command or prove that the record still exists. APIs that accept a UID separately may ignore this property and use their explicit argument.

Persistence and identity scope​

UID is mailbox metadata. GenerateHeader, ProcessHeaders, SaveToFile and LoadFromFile do not serialize or recover it. An .eml file cannot preserve the IMAP identity through this property.

A UID is meaningful only with the account/server, mailbox and the mailbox's UIDVALIDITY value. If UIDVALIDITY changes, cached UIDs from the earlier validity epoch must not be reused. Store that context alongside the string in durable integration state; UID alone is not a globally stable key.

Treat incoming UID text as untrusted protocol data when logging or building commands. Prefer the IMAP component's UID-aware methods instead of concatenating command strings. Concurrency still applies: another actor may delete or move the message after retrieval.

The example is source-reviewed only; no IMAP operation was executed.

External references

Created 2026-07-15