• I don't want to have a POP server on my Linode, I just want that, for example, the mail sent to me@mydomain.net is redirected to info@somethingelse.com and so on for a couple of email addresses. The destination email will take care of the rest (spam filtering, POP access, and so on).
• The email addresses I want to forward from my Linode to somewhere else are not necessarily Linux accounts.
• I don't want my box to be insecure and allow anybody to use it to relay spam everywhere.
• I know I have to set my MX record correctly to point on my Linode (I think I'm done here).
• No problem installing postfix if that's what I need (I heard it's safer than sendmail and even exim).
• I've got mySQL so I could use something like postfix-mysql is needed.
• I'm behind a firewall with only the minimum ports opened (of course!) and I'm not sure what's supposed to be opened for relaying the mail to my Linode.
• I'd like to send to a "blackhole" every mail for which I didn't specify a redirection (forward). I want something like:
  
  Code:

  user1@mydomain.net -> user1@whatever.com
  user2@mydomain.net -> user2@whatever.com
  info@mydomain.net -> user1@whatever.com
  other -> :blackhole: (or /dev/null)

virtual_users:
  debug_print = "R: virtual_users for $local_part@$domain"
  driver = redirect
  domains = +local_domains
  allow_fail
  allow_defer
  data = ${lookup{$local_part}lsearch*@{/etc/aliases-domains/$domain}}
  qualify_preserve_domain
  no_more

*: myreal@address.com

user1:    user1@otherplace.com
user2:    user2@otherplace.com
bad1:     :blackhole:
*:        catchall@otherplace.com

1. I've installed exim4, for some reason, I still had exim3.
2. I've added the 160_local_virtual_users in /etc/exim4/conf.d/router.
3. I've added the mydomain.com file (yes, with my own domain ) in the /etc/aliases-domains.
4. Is there another line to add to the main configuration?

1. I've sent emails to a valid user: nothing. No mail-delivery error, no forward.
2. I've sent emails to an invalid user: one of them returned a mail-delivery error after a *long* wait.
3. I've connected with "telnet mail.mydomain.com 25" to test the exim4 server. I can send a mail (all the answers are correct) but I didn't received it.
4. I've tried sending to another domain than my own and I have a message telling me I can't relay to this domain, good!

• The mail is forwarded to a completely different domain (I have mydomain.net (my linode) and mydomain.com (another)). When I want user@mydomain.net to be redirected to mydomain.com, I receive it in my linux account instead of on mydomain.com. Weird.
• On my system, I have the account user1 created. I've made 2 aliases, user1@mydomain.net and admin@mydomain.net. So admin does not match any account and when I try this email, I've got a "account does not exist" return mail.

user1:    someplace@else.net
admin:    somewhere@else.net

user1:      user1@elsewhere.com
admin:      user1
*:          :blackhole:

system_aliases:
  debug_print = "R: system_aliases for $local_part@$domain"
  driver = redirect
  domains = +local_domains
  allow_fail
  allow_defer
  data = ${lookup{$local_part}lsearch{/etc/aliases}}
#  user = list
#  group = mail
  file_transport = address_file
# pipe_transport = address_pipe
# directory_transport = address_directory