Getting bounced mail? here let me try and explain a few of the more common problems.
Have you added the domain to accept mail?
You need to add the domain into the mail server so it knows to accept email for it. If it accepts mail for every domain then its fairly easy for somebody to attack your server and fill up your hard drives. There is no one solution for this one at all because of the multitude of server setups and configurations.
For the basic Rimuhosting setup you can just edit /etc/postfix/main.cf and look for the line
mydestination = $myhostname, localhost.$mydomain, localhost
Add in any domains you want into here, usually it will have something like the above which should be left , just add a comma and append the new domain name.
If you are using virtual users then this will be virtual_mailbox_domains line possibly unless you are using a file.
Does the user exist?
Check that the user in the firstname.lastname@example.org actually exists. Did you add the user? check also that its all lower case at both ends, whilst english tends to make us want to use upper case, its generally a bad idea. Linux is case sensitive and this can cause problems.
Restarted mail server
So you added the user, checked the domain is in there, all configs checked and working, but did you restart the mail daemon? this can be usually done with
Check your MX record exists and points to a domain name. Then check that domain name points to your VPS IP address. An MX record can't point to just an IP address, some people add mail.domain.com and point that to the IP address which keeps things tidy.
Another thing to check, if you host your mail on gmail, and are having sending mail to your domain name from your VPS, often Plesk or Virtualmin or similar has added the domain to local DNS. This means it thinks that this machine hosts mail for you when in fact it may be elsewhere. The easy fix for this is to remove the DNS server for localhost. edit /etc/resolv.conf and remove or comment out the following line
Careful when upgrading
Often we have had emails that just suddenly 'stop working' and people have not upgraded or updated in a while, what they may have done is upgraded packages which overwrote configs. It pays to backup your working configs often, and check what packages are being upgraded.
If for any reason you get stuck and things break, just drop in a ticket for us to take a look and fix things.