I've followed the set-by-step located here:
http://library.linode.com/email/postfix ... _your_logs

and gotten to the check your logs step. After sending the test email and checking the log, i see:

Jun 23 03:31:57 li115-209 postfix/pipe[9727]: 95FEAA6B0: to=<first@medetis.com>, relay=dovecot, delay=0.04, delays=0.03/0.01/0/0.01, dsn=4.3.0, status=deferred (temp
orary failure)
Jun 23 03:39:01 li115-209 postfix/qmgr[9710]: 95FEAA6B0: from=<root@li115-209.members.lineode.com>, size=455, nrcpt=1 (queue active)
Jun 23 03:39:01 li115-209 postfix/pipe[9755]: 95FEAA6B0: to=<first@medetis.com>, relay=dovecot, delay=424, delays=424/0.02/0/0.07, dsn=4.3.0, status=deferred (temporary failure)

and I've no idea what to do from here.

looks like an issue with your dovecot, it might not processing the email requests.
check dovecot configs and mysql.

_________________
Linux Sysadmin
Ruby on Rails Developer

Please paste the contents of your dovecotlog.

$ tail -50 /home/vmail/dovecot-deliver.log

Set a hostname on your Linode and make an A entry in DNS for it. Then set reverse DNS for your IP to your hostname, in the Linode control panel. And then restart Postfix. Wait until all DNS changes have propagated and try the test again.

li115-209.members.lineode.com does not resolve. In today's spam-filled world you can't expect a remote mail server to accept mail from an unresolvable source.

- Your hostname should resolve to your IP
- Your IP should reverse-resolve to your hostname.

I fixed the unresolveable name, and a few other issues, and eventually found the problem -- I had made a small error in following the step-by-step tutorial, and upon redoing it from scratch fixed the problem.

Very time intensive, but I learned to be much more careful.

Which is why so many people do NOT host their own email server these days - instead use the free Google Apps.

Not only do they maintain it, but it's their storage and their bandwidth, and their expertise in Spam Filtering, etc.

If you think setting up Postfix was a pain, good luck it keeping it running smoothly, without malware, or spam, or getting your IP blacklisted (none of that is rocket science, but it does take a lot of time, and it's a never ending process).

For small domains (under 50 user accounts) I haven't run a SMTP server in-house for years. Don't miss it (or the hassle) a bit.