SMTP authentication - is it working properly

[fiver]

I have Enabled SMTP Authentication with the following options

Allow Login - If enabled, users will be able to authenticate themselves for relaying using a user and password

Allow Any Accounts Login Details - This option will enable the SMTP to accept a user and password from any local account for authentication. However, if an account is part of a group which does not allow ‘SMTP Authentication Access’, that accounts login details will not be accepted.

Allow Only The Following - (Not used)
User - (Not used)

Password - (Not used)

Yet my SMTP logs and outgoing mail appear to indeicate that losts of other people who are not my clients are able to send mail through my server. I cannot understand how this is happening - Can you please advise. My SMTP logs appear to fill up every 2 - 3 minutes.
Kind regards
Ivor

[rob]

I would recommend also examining your outmail logs to see if these mails are getting through as it is quite common for SPAM clients to probe and attempt to send mail via your server. However, if these are indeed passing through then there a few possible reasons why. The most common is that a username and password pair which is valid on your server is being abused, and so that user should be blocked or at least the password changed. Other possiblities include that POP Before SMTP authentication method is turning your SMTP into an open relay which can occur when some routers make all incoming connections appear to originate from the same IP address. In the meantime, I would recommend enabling the SMTP mail sending limits and also the group mail sending limits to contain the damage until it is resolved.