I am not an email expert, and I don't use Postfix. But two main things to check: First, there's the postfix activity log (/var/log/mail.log, /var/log/postfix*, or such). Check if there are lines inside with the timestamp matching your test email.
(Or, open the file, see the last lines, then send the email again, and read the ones that has been added since.
)
Paste them here.
Also, common caveat: If you send an email from gmail to a forwarder (or chain of forwarders) that'll in the end send it back to the originating gmail account, it'll disappear. I don't think there's official explaination for this, but the common guess is that they checksum the message, and "realize" a copy of it is already there (in your sent items box), so throw away the duplicate silently.
Never try to send test emails like this:
me@gmail.com => user@mylinode.net (or any other server) =forwarding=> me@gmail.com.
Use
account1@gmail.com => user@mylinode.net =forwarding=> anotheraccount25@gmail.com.