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ContentType

property ContentType: string read write;

Example​

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

  Msg.ContentType := 'text/html; charset=utf-8';
  // ContentType now reads text/html; CharSet reads utf-8.
end;

Usage​

ContentType stores the message media type while extracting charset, applying asymmetric empty defaults and controlling whether MIME type inference can run.

Additional Technical Info​

ContentType stores the message-level media type used for parsing and normal generated headers. Its setter does more than a raw field assignment: it removes an embedded charset parameter and updates CharSet under specific rules.

For nonempty input, the base value and other parameters remain in ContentType. A nonempty embedded charset replaces CharSet. With no embedded charset, text media defaults CharSet to us-ascii only when its current value is empty; otherwise the previous charset survives, even when changing to a non-text media type.

Assigning an empty String is asymmetric: the setter stores text/plain and sets CharSet to us-ascii. By contrast, ClearHeader writes the backing fields directly and leaves both empty. Reading empty is therefore possible after Clear, but ContentType := '' cannot reproduce that state.

Automatic MIME inference​

GenerateHeader infers a type only when Encoding is MIME and ContentType is truly empty. After recounting parts it chooses multipart/mixed, multipart/alternative or text/plain from text/attachment counts. Leave a new/cleared message value untouched to request this behavior; assigning empty disables inference by storing text/plain.

When generating a multipart message, a fresh boundary parameter is written into the header. The setter itself strips only charset, not a supplied boundary or arbitrary parameters. ProcessHeaders is different: it extracts charset, later removes boundary into MIMEBoundary, and defaults a missing type to text/plain; charset=us-ascii in typed state. It does not validate and replace a nonempty but syntactically invalid type.

Calculated single-part MIME clears the message-level generated content headers and lets its one part supply them. NoEncode ignores typed ContentType and writes raw Headers. No syntax or security validation is performed at assignment, so keep untrusted parameters out of raw header construction.

The example is source-reviewed only; no message was generated.

External references

Created 2026-07-15