Email software packages that provide native encryption of messages use proprietary algorithms and formats that are not compatible with other email software packages. This means that the encryption cannot interoperate across product domains, and the recipients of encrypted messages must use the same email software package as the sender to decrypt and read the messages. This limits the usability and scalability of native encryption, and may also pose security risks if the encryption algorithms or formats are not well-tested or widely accepted. A common drawback of email software packages that provide native encryption of messages is that the encryption cannot interoperate across product domains1234. References = CISM Review Manual 15th Edition, page 206. The Top 10 Email Encryption Solutions In 2023 - Expert Insights2, The Best Email Encryption Services for 2023 | PCMag3, The Top 12 Email Encryption Services for 2023 - Right Inbox4.

A common drawback of email software packages that provide native encryption of messages is that the encryption cannot interoperate across product domains. This means that emails sent from one product cannot be read by another product, as the encryption keys used are not compatible. This can be a problem when sending emails to people who use different software packages, as the encrypted emails cannot be read.