Individual messages in threads,
Links and attachments,
Instant Desktop Notifications

Track messages in threads

Use Gmail Scheduler to track email.

Download only allowed with password set by you (optional),
Prevent future downloads,
View download times.

Public, Private Key encryption using openpgpjs.org (PGP)
RSA or ECC curve encryption.
Or Symmetric AES 256 encryption.
How to encrypt using Public Key PGP or AES 256
Easy browser based key creation and management.
Encrypt and attach files.
Kodamail extension not required to decrypt AES 256, recipients can decrypt email at message decryption or files at: file decryption.

Public, Private Key encryption Or Symmetric AES 256 encryption using openpgpjs.org (PGP)
Encrypting a file using either Public Key PGP or AES 256-encryption
Easily encrypt or decrypt files files securely in Gmail, click on the kodamail tab in Gmail to start.
Virtually any file can be encrypted, want to encrypt a folder? just zip the folder and then encrypt it.
Not sure how to zip? this article show you: how to zip files in windows 10.

If you have created a Public Private Key pair, you can sign an email with your Private key and then the recipient can check the authenticity using the Public Key.
You can read more here: Signing an email.

Track email using Gmails 'confidential mode' (optional).
You can also encrypt an email and/or sign using confidential mode.

If subscribed under the 'Gold' plan you can link 3 additional gmail accounts to yours.
You can read more here:
Linking multiple gmail accounts