wildcards alias?

Hi

I'm interested in courier-mta, to build a custom server, mainly because 
it's C++ and modular, and looks interesting

the topic follow the 
https://sourceforge.net/p/courier/mailman/courier-users/thread/E1AWITI-0002fu-86%40sc8-sf-mx2.sourceforge.net/#msg16553149 
thread

I looked at .courier files but doubt they will fit my needs.

I want to provide wildcard alias to my users because today emails are 
used as login, so if a 3rd party server got compromised, the server can 
be attacked using the login information

so I want to provide user a login/password so that they can connect to 
webmail/imap/smtp and some wildcard alias

I don´t want to use the "obvious" [email protected] or 
[email protected] : it's not real "wildcard" anyone seeing the + 
or - know that the user is before and after is catchall

I saw that there is a configuration file to change the +/- char by 
another char, but I don't feel it interesting (one attacker gaining some 
email list can check if there is a single char that can be the 
delimiter) so I want my delimiter to be a string and that string being 
different for each user

my current email provider offers wildcard using * but at usage, it's too 
"flexible" and I can get email conflict (* matching any string of any 
length) (it seem to use postfix)

so I was thinking of something like

somestring....key...@mydomain : user
....user...key....eos@mydomain : user
user...key[x-z0-9]{min,max}@mydomain : user

in /etc alias configuration with . matching a single char, 
and [x-z0-9]{min,max} matching anychar min times and max times like in 
posix regex

.courier file don't seems to fit my need because it rely on finding the 
user by selecting the start of the email

I don't want that login@mydomain be usable (to prevent user spread login 
info on some web site)

is it possible?

is it possible to achieve using some custom filter program? (eg writing 
my custom "maildrop"), ie what happens to an email if the local user is 
not found? I don't want also to rely on "virtual" global user, it's too 
privacy problematic (one attacker obtaining access have access to all 
email of all users....), I prefer to manage my user permission (ssh, 
vpn....)

thanks and regards



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