fttUseExplicitTLS

fttUseExplicitTLS = 3

Example

function UsesOptionalStartTLS(Mode: TvxTLSType): Boolean;
begin
  Result := Mode = fttUseExplicitTLS;
end;

Usage

fttUseExplicitTLS requests an explicit STARTTLS-style upgrade but can continue plaintext when the server reports TLS unavailable.

Additional Technical Info

fttUseExplicitTLS is ordinal 3 of TvxTLSType. It maps directly to Indy utUseExplicitTLS for SMTP, FTP, POP3 and IMAP. The connection begins in protocol plaintext, discovers capability and then sends the protocol-specific upgrade command.

Despite its secure-sounding name, this is the optional mode. In the installed Indy client base, “TLS not available” defaults to continuing; Velox installs no override. The session can therefore proceed plaintext when a server does not advertise TLS, creating a downgrade risk. A rejected upgrade command or failed handshake raises by default, but absence of capability does not.

Use fttUseRequireTLS when encryption is mandatory. Certificate/hostname verification and permitted TLS versions remain separate settings.

The example only compares metadata and was source-reviewed; no STARTTLS, downgrade, network, certificate, runtime or image test ran.

External references

• Indy TIdUseTLS source.

Created 2026-07-15