[Dovecot] FTS autoindex username problem

[lee_yiu_chung at yahoo.com]

I tried to set up Solr search server according to http://wiki2.dovecot.org/Plugins/FTS/Solr, and 
turned on autoindexing according to http://wiki2.dovecot.org/Plugins/FTS, but I found a strange 
behaviour that cause server search missing some emails.

Here is the login information of my mail server:
version: 2.2.12
login name: user1
email: user1 at example.com

Now, when I turned on autoindexing, all autoindexed email are indexed using user1 at example.com as 
username key, as shown in maillog:

dovecot: [ID 12345 mail.info] indexer-worker(user1 at example.com): Indexed 1 messages in INBOX

But when I triggered on-demand indexing using IMAP server search, the emails are indexed using user1 
as username key instead, as shown in maillog:

dovecot: [ID 12345 mail.info] indexer-worker(user1): Indexed 1799 messages in INBOX

Only the emails indexed using user1 can be searched, emails indexed using user1 at example.com cannot 
be found. How can I configure autoindex to index email using user1 as username key?

---
(Below is a follow-up question)

In my mail server config, there are a few virtual mailbox users are using the following login 
information instead (different auth/password backend):
login name: user2 at virtmail.example.com
email: user2 at virtmail.example.com

In this case, how can I distinguish user1 at example.com and user2 at virtmail.example.com, so that emails 
for user1 at example.com can be indexed using user1 as username key, while user2 at virtmail.example.com 
can be indexed using user2 at virtmail.example.com as username key?