I went back and deleted the fijatevos.com and fijatevos.com line from the
/etc/postfix/virtual, That was what Joe meant, right?
"Virtualmin manages those entries for you...so you shouldn't be adding them manually"
You left off part of that quote…the most important part, I think:
“unless Virtualmin wasn’t there for the initial creation of the user”
Virtualmin can’t create them if it wasn’t working when you created the domain or setup the users, either because it wasn’t installed yet, or because it wasn’t configured correctly. Virtualmin does not (yet) have time travel or mind reading capabilities.
So I am looking at (but not touching) the main.cf file - I have this setting:
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
below that line is a line commented out:
#mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain,
# mail.$mydomain, www.$mydomain, ftp.$mydomain
Maybe I am missing the second line? I can add that in Webmin and see.
No. You do not want mydestination to be where virtual domains are configured. Virtual domains should be configured in the virtual maps file only.
You do not want your virtual domains listed in relay_domains or mydestination (and actually, I guess mydestination is the directive I meant to mention the first time…it’s been a while since I’ve setup postfix in the non-virtual maps way). I mentioned this stuff only because I assumed your system was incorrectly setup to use them instead of virtual maps. Do not go poking around and sticking stuff in those directives–you aren’t using them for your virtual domains, at all.
The relevant configuration for virtual hosting in Postfix:
virtual_alias_maps = hash:/etc/postfix/virtual
That’s it! If you have a bunch of extra stuff related to your virtual servers anywhere in main.cf, it is wrong. Everything related to your virtual domains goes in /etc/postfix/virtual (and, if Virtualmin is creating your domains for you, it will manage this file). And everything correctly configured in the virtual maps file becomes an acceptable destination.
Every virtually hosting domain needs a line like:
virtualmin.com virtualmin.com
In the virtual maps file. And every user needs a line like:
joe@virtualmin.com joe.virtualmin
Again, this is not something you should normally be creating manually–but if you’re adding Virtualmin to a system with existing users, they do need to be setup correctly, or they won’t work–Virtualmin isn’t going to try to figure out what you were trying to do and fix incorrect configuration for you–it can’t read your mind. 
This is why we have an install script to setup the system for virtual hosting. There are a lot of steps, touching a lot of different software, and if you don’t know how they all work, it’s going to be complicated.
If this system isn’t in production yet, you might want to start over with a freshly installed supported OS and run our install.sh script. It’ll setup all of this stuff for you, and it will pretty much just work out of the box.
I’m kinda confused about what you’re trying to do, and what you’ve done so far (I’m easily confused), so I’m having a hard time even telling you what to do to correct the old broken configuration and get to something sane. Starting from a fresh, default, Postfix configuration file is probably another good option. Or you could post your whole current postfix configuration (“postconf -n” will show just the non-default settings).