I hope someone can help me with this please.
One of our clients has an in-house Postfix mailserver which basically downloads mail for the individual users from our mail server hosted on the web using fetchmail. They use our SMTP server to send mail. Their email clients are then setup to get & send mail from the server, on 192.168.2.254 (for POP3 & SMTP). All mail between them on the local LAN gets send to each other via the server, and not the internet.
This works quite well, but as soon as someone sends mail from the Linux server directly (it has webmin + usermin installed and has a basic webmail interface for when they're out of the office) it sends mail using the local machine name, instead of the domain name. for example, mail comes from email@example.com.
How do I tell Postfix to automaticlly send mail from @<theirdomain.com> instead?
Sorry for asking this, but I don't know Postfix very well and don't know what to call to, to search on google.
So, is the user's username in the above case "esther"?
If so -- the issue may just be that Usermin needs to be configured with the actual username.
How Usermin determines that is setup in Webmin -> Usermin Configuration -> Read Mail, in the "User From addresses" section.
On my system here, it's setup to use /etc/postfix/virtual to determine that (which is what you'd see on a server running Virtualmin).
In that file, you'd basically have a series of lines like this:
That should setup a mapping that Usermin can use in order to determine what all the "From" addresses should be.
How do I tell Usermin to automatically add new users to that file?
Well, it should by default... any time you add a new Virtual Server, or a new email user, it should add entries to the virtual file.
Are you using Postfix on your system?
I do use Postfix, but the only mappings in that file are which I have added myself some time ago
Ah, I bet you're not using Virtualmin on that system, are you... Virtualmin would automatically add those entries for you. But, if you're simply adding users to the server via Webmin or on the command line, that wouldn't populate the virtual file.
In that case, you may actually find RoundCube simpler, as you can easily set the "From" address for each account.
Otherwise, you'd need to make sure you populate the virtual file each time a user is added to the system... or install Virtualmin, and use it to add your users to the server.