[Dovecot] How to add the missing maildir folders

[Egbert Jan van den Bussche]

Hi fellow list members,

What would be the best way to add the .Sent,.Draft, etc. folders to the 
maildir tree? It seems not Dovecots task to do that but of the MUA.

I have seen several options. Use of skel but that works only for new 
system users. I have only virtual users preloaded in a database. I've 
discoverred that ONLY Roundcube add the folders (if configured to do 
that) but I've not been able to have the folders created by Thunderbird. 
Yes, you can manage the subscribtions to folders but there is no way to 
create them. I did not bother to try Outlook... MY users use pop3, imap 
and web (Roundcube) but I cannot ask them to use Roundcube first, just 
to create the folders.

I have no such thing as maildrop, which seems to be able to create 
folders. Should I run some script during login? How?

TIA
Egbert Jan (NL)