%u               user@domain
%n               user
%d               domain
%s               imap, pop3, smtp, lda
%l               local IP address
%r               remote IP address

%h                home directory
%i                uid
%w                plaintext password 

Modifiers

%L - lowercase
%U - uppercase
%T - Trim trailing whitespace

e.g. %Us = POP3

%%?

%%             '%' character

%var expands to the logged in user's variable, while %%var expands to the other users' variables.

e.g.

當要取得 %%h 時, Dovecot 會透過 dovecot-auth 去問 auth-master socket