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UseNowForDate

property UseNowForDate: Boolean read write;

Example​

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

  // If currently dynamic, capture Now once into Date.
  Msg.UseNowForDate := False;
end;

Usage​

UseNowForDate exposes whether Date is the zero sentinel and controls whether generation reads the current clock repeatedly or captures it once.

Additional Technical Info​

UseNowForDate controls whether normal message generation uses a stored Date or reads the current local clock. It is not backed by its own Boolean field. Its getter is exactly equivalent to:

Result := Msg.Date = 0;

The setter changes Date only when the requested Boolean differs from the current derived state:

AssignmentEffect
True while currently falseSet Date to 0.
False while currently trueSet Date to Now once.
Assign current value againNo change and no new clock read.

Consequently, assigning Date directly also changes UseNowForDate. There is no state in which UseNowForDate is false and Date is zero.

Dynamic versus fixed generation​

When UseNowForDate is true, GenerateHeader reads Now into a temporary and formats it. Date remains zero. Every later generation, send or normal save can therefore produce a new header timestamp.

When false, generation uses the stored nonzero Date. Changing true to false is a convenient way to capture the current time once, as shown in the example. Reassigning false later does not refresh that timestamp; set true and then false, or assign Date explicitly, if a deliberate refresh is required.

This distinction matters for deterministic retries, message signing, idempotent archives and comparisons. Freeze the value before the first output when repeated byte-level generation should not change solely because time passed.

Clear, load and raw output​

ClearHeader assigns Date zero, so UseNowForDate becomes true even though its setter is not called. ProcessHeaders sets Date from the incoming header. A missing or unparseable Date can produce zero and re-enable dynamic generation; a later normal save may then add the current date rather than preserve the absence/invalid value.

NoEncode bypasses GenerateHeader. UseNowForDate and Date do not affect the raw output in that mode.

The current-time read uses the Velox process's local environment. Clock accuracy, time-zone configuration and daylight-saving behavior are host concerns. See Date for the current-offset formatting quirk.

The example is source-reviewed only; no clock-dependent message generation was executed.

External references

Created 2026-07-15