Deoplete-notmuch offers asynchronous completion of email addresses using notmuch address.
Based on @paretje's deoplete-notmuch, which was inspired by @fszymanski and @frbor's abook sources.
To install deoplete-notmuch, use your favourite plugin manager.
Using vim-plug on neovim
Plug 'Shougo/deoplete.nvim', {'do': ':UpdateRemotePlugins'}
Plug 'Valodim/deoplete-notmuch', {'for': 'mail'}" notmuch address command to fetch completions. in theory, any command that
" outputs addresses one per line is compatible.
" must be --format=text. note that --output=recipients is very slow!
let g:deoplete#sources#notmuch#command = ['notmuch', 'address', '--format=text', '--deduplicate=address', '*']