Is possible to override Dovecot variables or Sieve env vars and extdata lookups

[MRob]

On 2018-03-19 06:31, Aki Tuomi wrote:
> On 19.03.2018 06:40, MRob wrote:
>> Are the dovecot environment variables mutable? I'd like to override 
>> like:
>> 
>> set "${env.vnd.dovecot.username}" "someuser at example.org"
>> 
>> Or better, I prefer to override %u Dovecot variable during the userdb
>> lookup.
>> 
>> Is either possible?
>> 
>> PS, when Sieve does extdata lookups for username key, where does
>> username come from? %u?  Does an override as above change the dict
>> lookup key for extdata?
> 
> You could override the %u variable, but overriding it in userdb will
> have surprising consequences. Basically this amounts to same as 
> changing
> username for the user.

This is useful to work with a older system in my case, username should 
seem as a new one anyways. I accept the consequence. :)

I tried return only "u" in the passdb and usedb lookup (also "userdb_u") 
but it did not work. Where can I override %u? Can I do it in both passdb 
and userdb lookup?