Not really. iMessage is reasonably secure, but only when compared to standard SMS, MMS, and email — and only when communicating with someone else who is also using iMessage.
Something like Signal, Wire, or Telegram would be better for messaging — and in that order for security. Proton Mail or Tutanota are good options for encrypted emailing. I would recommend Proton over Tutanota, because it offers a more secure login (one password to get into you account, another for each inbox), and Proton also offers a way to send PGP mail to non-Proton users.