Safer Internet: Email: Anonymity, Encryption

Summary

If content and/or sender/receiver are extremely sensitive, additional measures may be desired beyond encryption during transit of message and attachments via HTTPS:.
[2] Send files encrypted separately via email but transmit key via non-email-- see Encryption section, e.g., 7-zip
Transfer via cloud or other sharing method -- see Share Files Privately
[3] Encrypt email messages using PGP or S/MIME (requires certificate) -- or other services, e.g., Lavabit
iOS: Settings > Accounts & Passwords > Account > Advanced > S/MIME
[3] Send email anonymously, e.g., specialized providers
[3] Use self-destructing email -- never stored on recipient's system

{TCYOP-4: 125-131; TCYOP-3: 101-108; S/MIME; PGP/OpenPGP/GnuPG: SecureMyEmail; Proprietary encrypted email: Peerio, ProtonMail, Tutanota; Encrypted attachments; Transferring Passwords Out of Band: in person, by phone, by chat or private message, via shared knowledge; Send and Receive Email Anonymously; Use Email Alternatives; 'self-destructing' messages}
sections: Refs: iOS; macOS; see Browsing: Tor, NSA
Wikipedia: Email encryption; S/MIME (Secure/Multipurpose Internet Mail Extensions) requires key/certificate
Wikipedia: GnuPG (Gnu Privacy Guard) aka GPG; open source; GPGTools/GPG Suite: encrypt, decrypt, sign and verify files or messages
Wikipedia: Snapchat user set time limit for viewing photos/videos
How to send anonymous emails PC; 3/4/2019