[exim] SPA Authenticator: using @ in Outlook username does n…

Hello,

I am having some issues using a username@??? kind of username in
Outlook and the Exim SPA authenticator.

It seems the domain part is stripped from the username and so I cannot
authenticate properly.

Is this a known problem? Can I fix this issue in any way?

On debug I find that a username like: username+domain.tld is passed
completely to the exim $auth1 variable, but with the @ in place I only get
the username part without the domain.

I have to consider that I am using the same username for Dovecot, so I
cannot just change my query to replace @ with something else.

Authenticator config:
SPA:
driver = spa
public_name = NTLM
server_password = ${lookup mysql{SELECT `password` FROM `users` WHERE
CONCAT_WS('@', `username`, `domain`) =
'${quote_mysql:$auth1}';}{$value}{fail}}
server_set_id = $auth1
server_debug_print = "Running SPA auth: $auth1"

Thank you,
Jan