I have on machine that does not have GW client, but has only Outlook

It is only used for SMTP sending mails via GWIA

It works fine to external sources, but to internal ones it only works for
some users, for majority it does not work

It probably it is something with access control (can not understand how &

Can see in the log that the mail being send, but it never arrives in
internal user (same domain) mailbox

No error visible