I took that to read that they "
can't" send.
One thing to check is if they are genuinely authenticating. To check this, you need to enable debug logging in the SMTP Relay. Edit /var/opt/scalix/sys/smtpd.cfg and add the line
You will need to restart the SMTP Relay service
for this change to be picked up. The file
/var/opt/scalix/tmp/smtpd.log will contain all of the SMTP conversations from sending clients/MTAs. The caveat to this is that if the file gets above 2Gb in size, it will cause problems so, enable the logging, get one of the problem users to send a message and then disable logging again.
You should be able to see if any successful authentication takes place. One thing to point out about Thunderbird is that it will attempt a couple of authentication methods to see which one succeeds before it returns any kind of error back to the client.
Cheers
Dave