Notifications are shown as
Sent in BA providers control panel, but the customers (or the specific ones) state they do not receive it.
Check what mail server is used:
Make sure the host from the file processes e-mails correctly.
For example, if you see
[Server] Host = localhost Port = 25
that means that local mail server is used to send the notifications, check /var/log/maillog on the BA application server to check the notifications sending status. If some other server is used, check the maillog on the related server. Mail is not part of BA, if notification is shown as "Sent", that means BA did its part of job, please contact your system administrator to check the maillogs.