If a client isn't allowed to establish a connection to the server it won't even be able to try to authenticate. To prevent unwanted relaying I would suggest checking both "Use strict local relaying restrictions" and "Authenticated SMTP Connections may relay mail" to have all clients connecting from a mobile device or otherwise from a not trusted IP address authenticate. If you want users on your trusted IP ranges to be able to send mail without authenticating you can check "Connections from this address range may relay mail through this server" for each trusted range.

Hello, 

we are using Mercury v4.73 as our customer mail server. Our Mercury SMTP server is using IP address ranges for the connection control. Only our clients can use the SMTP server.

A lot of our customers are now using smartphones to retreive their emails. However, they cannot use the SMTP server to send emails because they are not in the allowed IP ranges. And we have different mobile carriers so it is too complicated to whitelist every ip addres in the connection control section.

So we created a SmtpPW.txt file and we activated the "Authenticated SMTP Connections May Relay Mail" option. But it seems the Connection Control is still blocking the SMTP communications even if the client is specifying a SMTP username/password.

So my question is : How can I allow unknown IP address comming up from cellphones carriers without having to allow every possible IP addresses in the Connection Control ? I don't want my server to be a SMTP open relay ...

Is the "Only Authenticated SMTP Connections may relay mail" option is my only choice ? 

FYI I have more than 5000+ email accounts so I hope there is a way to allow SMTP authentication before doing the connection control verification .. otherwise we will have a lot of calls from our customers ...

thank you for your help on this matter !