feat: add terminal email with aerc + notmuch + mbsync + M365 OAuth2

Summary

Set up terminal email using aerc as the frontend, with full offline support and M365 OAuth2 authentication.

Proposed stack

sbfnk/M365-Auth  (OAuth2 tokens → macOS Keychain)
       │
       ├──→ mbsync (IMAP sync → local Maildir)
       │         ↓
       │    notmuch (search/tag index)
       │         ↓
       │    aerc (notmuch backend — read, search, tag)
       │
       └──→ msmtp + msmtpq (SMTP sending + offline queue)

Components

Config files to create

~/.config/
├── aerc/
│   ├── accounts.conf    # Account source/outgoing/credentials
│   ├── aerc.conf        # UI, filters, hooks, compose settings
│   ├── binds.conf       # Keybindings (vim-style)
│   └── stylesets/       # Theme (catppuccin)
├── m365auth/
│   └── config.py        # Client ID, scopes, authority URL
├── notmuch/
│   └── default/config   # Database path, user info, new mail tags
├── msmtp/
│   └── config           # SMTP account with xoauth2 auth
└── mbsync/
    └── mbsyncrc         # IMAP channels, Maildir paths, PassCmd
~/Mail/                  # Local Maildir root
~/Library/LaunchAgents/
├── mail.sync.plist      # Periodic mbsync + notmuch new
└── mail.sendqueue.plist # Periodic msmtpq flush

Why this architecture

• aerc as frontend — vim keybindings, runs in tmux pane/popup, uses neovim for composing
• notmuch backend (not raw IMAP) — full offline access, fast local full-text search, tag-based workflows
• mbsync for sync — battle-tested IMAP-to-Maildir. Seb's custom isync formula adds XOAUTH2 SASL support
• Seb's M365-Auth for OAuth2 — Python + macOS Keychain + Thunderbird client ID. No Haskell (oama) or GPG (mutt_oauth2.py) needed. refresh-token --profile mail slots into mbsync PassCmd and msmtp passwordeval
• msmtpq for offline sending — queues outgoing mail when offline, flushes via LaunchAgent
• Backend is identical to sbfnk/dotfiles (mu4e swapped for aerc) — Seb can help debug

tmux integration

Add a popup keybinding similar to gh-dash:

bind-key M display-popup -E -w 90% -h 80% -d '#{pane_current_path}' 'aerc'

Open questions

• Confirm IMAP is enabled on M365 tenant (if not, need DavMail gateway)
• Single account (work) or multiple accounts?
• Decide on catppuccin or tokyonight styleset for aerc

References

• aerc wiki: M365 provider
• aerc + mbsync + postfix offline guide (Drew DeVault)
• aerc notmuch integration
• sbfnk/M365-Auth
• sbfnk/homebrew-formulae (custom isync)
• Ben Swift 2025 email yak-shave
• Catppuccin aerc theme

This was opened by a bot. Please ping @seabbs for any questions.

Start by resolving the open questions about M365 IMAP access, account count, and the aerc styleset. Then review the listed configuration paths under ~/.config/ and ~/Library/LaunchAgents/, along with the aerc, mbsync, notmuch, msmtp, and M365-Auth references. Done means the terminal mail stack is installed, configured for offline sync and sending, and integrated with the proposed tmux popup.