Relaymail: PGP Encrypted Email

relaymail keeps your OpenPGP private key where it belongs: on your
YubiKey. Tap to decrypt encrypted mail or sign outgoing messages —
your secret key never touches the phone.
WHY HARDWARE-BACKED?
Most "PGP for mobile" apps either don't decrypt at all, or copy your
private key onto the device. relaymail does neither. Every private-key
operation runs on the YubiKey itself: the app hands the ECDH (cv25519)
or RSA decryption to the card, which does the math and returns the
session key. Signing — Ed25519 or RSA — is also performed on-card.
Without the YubiKey in your hand, encrypted mail stays sealed and
signed mail can't be forged in your name.
KEY FEATURES
Decrypt and sign on the YubiKey: ECDH cv25519 + RSA for decryption,
Ed25519 + RSA for signing
Send encrypted and signed mail using your recipients' public keys
View and preview attachments — PDF, images, plain text, Office
formats and more, with the iOS share sheet for save-to-Files
and open-in-other-app
Paperclip indicator in the inbox so you can spot mail with
attachments at a glance
Multiple accounts in one app, plus a unified inbox across them
Auto-configuration for iCloud, Gmail, Microsoft, Yahoo and Fastmail
Microsoft 365 and Outlook.com accounts sign in with OAuth2 — no
app password needed
Web Key Directory (WKD) lookup to find recipients' public keys automatically
Auto-import of public-key attachments from incoming mail
Reply, Reply All and Forward with proper threading headers
(In-Reply-To / References) and quoted-original formatting
Swipe to mark read/unread, flag, archive, move to junk, or
delete — like the system Mail app
iCloud sync of accounts and imported public keys across your
devices, end-to-end through your private CloudKit container
Background fetch with new-mail notifications and an unread badge
on the icon
Address autocomplete from your iPhone contacts
Available in English and Spanish
WHAT YOU NEED
iPhone with NFC (iPhone 7 or newer), or iPad with USB-C
A YubiKey 5 NFC for iPhone, or a YubiKey 5C / 5C NFC for iPad,
with the OpenPGP applet provisioned
Email account credentials — iCloud, Gmail, Yahoo and Fastmail use
app-specific passwords; Microsoft accounts sign in via OAuth2
PRIVACY
Your private key never leaves the YubiKey. Period.
Public keys are stored locally on your device and (optionally)
mirrored to your private CloudKit container so a second device
sees the same keyring.
Account passwords are stored in iOS Keychain (synced via iCloud
Keychain if you have it on).
Your contacts are read locally for autocomplete and never sent
anywhere.
No analytics. No tracking. No third-party servers.
Built for OpenPGP users who don't want their private key on the phone.