Concernant la fonction relayhost

Yes, that should work as well. Just don't set a username and password.

 

That's the answer @Croydon gave you already, but probably you want to know something else that you did not ask for. He told you how you can relay trough an ISPConfig server which is the most obvious answer as you are asking in the ISPConfig forum. Just a wild guess, maybe you want to relay through another service a not ISPConfig? In that case, you should contact that other service and ask them for their requirements.

In case you want to use an external smtp relay service and not relay trough ISPConfig, then you can set that external relay service under system > server config > mail in ISPConfig. You can leave the password and user field empty when that service does not require a username or password. Otherwise, you can enter one username and one password there as only one service for the whole system is supported. if you want to use multiple relay hosts, then you'll have to setup this manually in postfix.

 

No. Have a look at the postfix documentation for details on how to configure postfix for multiple relay destinations.

 

Yes, might work. Try it out.

 

You still did not explain in detail what you are trying to do, which makes it impossible to say if the changes you made now are the correct way to achieve that goal. In general, the setup you posted looks correct in case you are trying to relay from your ispconfig server through multiple third party systems where the external relay is chosen by domain name, but as mentioned earlier, we have no howto on that topic here at howtoforge if multiple external systems should be used as relay, so you have to look for a general postfix config and I will not start installing a server to test such a config for you, so you will have to debug that yourself on your own server.

 

The relay function is not a function to direct email for unconfigured addresses to a different server. The relay function exists to configure that email which is sent from your server (the sender must be allowed to send from the server, see the post from @Croydon) by using a different external relay system.

Example: you have configured the email domain example.tld and example2.tld and some mailboxes for both domains on your server in ISPConfig. Now you want that email of users with an @example.tld address is sent directly by your server but email for accounts at example2.tld like a user which has the address [email protected] is sent trough mail.smtp2go.com (maybe because he sents newsletters and you don't want to get blacklistings for your mail system). In this case, you use such a relay config as shown in the link you posted. But as I mentioned already, this is not related to unconfigured addresses, relaying is the routing of outgoing emails trough a specific server but the users which send the emails must be allowed to do this by either authenticating via smtp-auth on your server or by sending from localhost on the server or by sending from an IP address which is listed in mynetworks in postfix main.cf.

 

I guess we're getting nowhere in this thread. Maybe someone else wants to explain to you in his words what a relay host is and what it is used for as you don't seem to understand my explanations.

 

I'm not angry, I'm just realistic that we both waste our time in this thread if we continue posting because you know what to set up, the tutorial from necrux.com shows it in detail plus I explained here when this relay setup can be used and which requirements must be met so you can check if a relay is really what you need to achieve your goals, so there is simply nothing more to be said. The next steps for you are, check your config again against the tutorial from necrux.com, e.g. that you used the right user credentials and domain in smtp_sasl_password_maps file, the domain there is the relay target domain and not your domain and that you used the correct syntax like wrapping the domain in [] and using the right port and use postmap to compile the file etc.