Email server can receive but not send

Is your firewall blocking connections from your home to your linode's port 25? (This is different from telnet'ing from the same machine.)

Does your ISP block port 25? (Many ISP's do. In that case you need to set up Postfix to listen to a different port.)

Your server looks fine to me - I think it is probably your client machine that is causing your problems.

Try disabling any local firewall on the client machine?

Are you telnetting from the client machine, or from the server itself?

P.S. Once you get things working, for security you should consider disabling plaintext auth unless you make a TLS connection:

smtpdtlsauth_only = yes

Authenticated mail submission is typically done on port 587 now, so you should make sure your firewall permits that. A quick test shows that you currently are not allowing connections to 587.

Thanks, the problem was on the client side. Thanks for the help in fixing that. Sorry for the slow response (I am actually on vacation).

Thanks again!