System.Object
   Dart.Mail.ContentType
   Dart.Mail.DeliveryStatusNotification
   Dart.Mail.HeaderField
   Dart.Mail.HeaderKey
   Dart.Mail.ImapResponse
   Dart.Mail.ImapSearchParameter
   Dart.Mail.MessageBase
      Dart.Mail.ImapMessage
      Dart.Mail.PopMessage
   Dart.Mail.Part
      Dart.Mail.Multipart
         Dart.Mail.MailMessage
      Dart.Mail.Resource
         Dart.Mail.Attachment
         Dart.Mail.Messagepart
         Dart.Mail.Textpart
            Dart.Mail.Htmlpart
   Dart.Mail.Proxy
   Dart.Mail.Recipient
   Dart.Mail.Security
      Dart.Mail.ClientSecurity
         Dart.Mail.MailSecurity
   Dart.Mail.Segment
      Dart.Mail.Data
   Dart.Mail.Session
      Dart.Mail.TcpSession
         Dart.Mail.AuthenticatedSession
            Dart.Mail.MailSession
               Dart.Mail.ImapSession
               Dart.Mail.SmtpSession
   Dart.Mail.SmtpResult
   Dart.Mail.SocketOption
      Dart.Mail.TcpSocketOption
   System.Collections.Generic.Dictionary<TKey,TValue>
      Dart.Mail.HeaderDictionary
   System.Collections.Generic.List<T>
      Dart.Mail.Mailbox
      Dart.Mail.MailboxCollection
      Dart.Mail.MultipartContent
      Dart.Mail.PartCollection<T>
      Dart.Mail.PopMessageCollection
   System.EventArgs
      Dart.Mail.BaseEventArgs
      Dart.Mail.ErrorEventArgs
      Dart.Mail.ImapAlertEventArgs
      Dart.Mail.ImapUpdateEventArgs
      Dart.Mail.ProgressEventArgs
         Dart.Mail.ImapProgressEventArgs
         Dart.Mail.PopProgressEventArgs
         Dart.Mail.SmtpProgressEventArgs
      Dart.Mail.UserStateEventArgs
         Dart.Mail.DataEventArgs
   System.Exception
      Dart.Mail.DartLicenseException
      System.ApplicationException
         Dart.Mail.DataException
         Dart.Mail.PipelineSendException
         Dart.Mail.ProtocolException
   System.MarshalByRefObject
      System.ComponentModel.Component
         Dart.Mail.ComponentBase
            Dart.Mail.MailBase
               Dart.Mail.Imap
               Dart.Mail.Pop
               Dart.Mail.Smtp
            Dart.Mail.SocketBase
               Dart.Mail.TcpBase
   System.Net.EndPoint
      System.Net.IPEndPoint
         Dart.Mail.IPEndPoint
   System.Net.Mime.ContentDisposition
      Dart.Mail.ContentDisposition
   System.Text.Encoding
      Dart.Mail.ImapUTF7

Reference

Dart.Mail Assembly