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ProcessHeaders

procedure ProcessHeaders;

Example​

procedure ParseReplacementHeaders(const Message: TIdMessage;
  var Value: Variant);
begin
  Message.ClearHeader;
  Message.AddHeader('Subject: Example message');
  Message.AddHeader('Content-Type: text/plain; charset=utf-8');
  Message.ProcessHeaders;
  Value := Message.Subject;
end;

Usage​

ProcessHeaders projects the current raw Headers into typed message state using Velox decoding, defaults, priority precedence and MIME-layout selection.

Additional Technical Info​

ProcessHeaders reads the current raw registered-but-ungenerated Headers list and replaces/normalizes the corresponding typed message properties. It does not parse body bytes and does not remove the raw lines.

Content-Type receives special handling. A missing/empty header becomes text/plain with us-ascii. A present value has its charset parameter removed into CharSet; a text media type without a charset also defaults to us-ascii. Later, the method removes the boundary parameter from the stored ContentType and pushes its value into MIMEBoundary with parent -1.

It copies Content-Transfer-Encoding and Content-Disposition, MIME-decodes Subject and address display names, and replaces FromList, To/Recipients, Cc, Bcc and ReplyTo through Indy's permissive address parser. Message-ID and In-Reply-To pass through their bracket-normalizing setters. Newsgroups are parsed as comma-separated text. Organization, Sender and receipt-recipient text are assigned without the same encoded-word decoding used for Subject/address names.

Receipt address precedence is Disposition-Notification-To, then Return-Receipt-To only when the first parses to empty text. Date is converted from the header's GMT/RFC form to local TDateTime. Invalid values can raise or normalize according to the underlying Indy routines.

Priority precedence is exact: X-Priority, Priority, Importance, then X-MSMail-Priority. Text containing non-urgent or low becomes mpLowest; otherwise text containing urgent or high becomes mpHighest; otherwise the first token is parsed as 1..5 with invalid/out-of-range input defaulting to 3 (mpNormal). Intermediate mpHigh/mpLow values are obtained only from numeric 2/4.

Encoding is selected solely from MIME-Version: absent means mePlainText, present means meMIME. The Encoding setter consequently selects UUE or MIME AttachmentEncoding. A boundary without MIME-Version still yields plain-text layout; MIME-Version without a boundary yields MIME layout, matching the source TODO rather than a stricter MIME inference.

Important quirk: the method does not clear MIMEBoundary before pushing. Normal LoadFromStream calls Clear first, but repeated direct ProcessHeaders calls can accumulate boundary entries; a later header with no boundary leaves an existing stack untouched. ClearHeader/MIMEBoundary.Clear before reparsing a replacement header set.

The projection is sequential and non-transactional. A malformed later field can leave earlier properties/lists already replaced. Complexity is linear in header/address content plus decoder work, and the message is not thread-safe. The source-reviewed example establishes a clean header state first and was not runtime-tested.

External references

Created 2026-07-15