Migrating "fake" virtual domains to proper virtual domains

Hello everyone,

aeons back, when I first set up or mailserver, cyrus did not support virtual domains. We used phpcyradm (if anyone remembers) and its approach to have user names encoding the domain + some identifier. 

So, nearly 20 years later, people are becoming really confused when I tell them that they cannot use their email address to log in but need to use this weird clunky thing I gave them.

I would like to migrate it properly now. My question is, can I migrate the mailboxes to the new scheme while having people being able to use the old, generated username and their mailaddress? 
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Cyrus: Info
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