IMailTransportSendAsync Method (FormatOptions, MimeMessage, CancellationToken, ITransferProgress)
Task<string> SendAsync( FormatOptions options, MimeMessage message, CancellationToken cancellationToken = default, ITransferProgress progress = null )
Asynchronously sends the specified message.
The sender address is determined by checking the following message headers (in order of precedence): Resent-Sender, Resent-From, Sender, and From.
If either the Resent-Sender or Resent-From addresses are present, the recipients are collected from the Resent-To, Resent-Cc, and Resent-Bcc headers, otherwise the To, Cc, and Bcc headers are used.