simple postfix configuration - forward all incoming email to single address

I've a Ubuntu 9.04 server installation which is hosting a small number of websites (currently two, and will remain in single figures). The email requirements for the server are very limited - to send outgoing emails and forward all incoming emails to a mailbox on another server - most likely Google.

I've installed postfix and the outgoing mail is working fine. How do I configure Postfix to forward all incoming mail? If I send it to a googlemail address are there any special considerations? Finally how difficult is it to incorporate basic spam filtering into the forwarding mechanism?

This is called a "catch all"

Mapping is done using /etc/postfix/virtual file.

vi /etc/postfix/virtual

Append code as follows, replacing domain and emailusername with actual values:

@yourdomain.com emailusername

Save and close the file. Run following command:

postmap /etc/postfix/virtual

Also make sure you have following line in /etc/postfix/main.cf file:

virtual_alias_maps = hash:/etc/postfix/virtual

If you just added above, line reload postfix:

service postfix reload

From http://www.cyberciti.biz/faq/howto-setup-postfix-catch-all-email-accounts/

You need virtual aliases. Something like:

virtual_alias_domains = foo.com, bar.com
virtual_alias_maps = hash:/etc/postfix/virtual

where /etc/postfix/virtual contains:

@foo.com    [email protected]
@bar.com    [email protected]

run postmap /etc/postfix/virtual to create the database from the map file and postfix reload to re-read the configuration. The virtual table is quite flexible -- you can match specific addresses or whole domains and forward mail to multiple addresses.

Note: Do not list the extra domains in $mydestination! See the docs for more detail.

No special considerations I can think of when sending to GMail addresses. One optional neat trick is to send mail for each domain to a separate address and have GMail automatically label it accordingly. Forward mail for foo.com to [email protected] and bar.com to [email protected] and corresponding filters. See this GMail blog post for more.

I haven't tried but one method to filter spam is to incorporate SpamAssassin. A Google for this turns up quite a few handy-looking guides.