diff --git a/src/content/docs/ispmail-trixie/160-receive-emails.mdx b/src/content/docs/ispmail-trixie/160-receive-emails.mdx index 0ea3c79..da7e63b 100644 --- a/src/content/docs/ispmail-trixie/160-receive-emails.mdx +++ b/src/content/docs/ispmail-trixie/160-receive-emails.mdx @@ -76,4 +76,139 @@ servers may be more likely so flag your sent emails as spam if you do not have a ## Postfix -… +Now that other mail servers can locate your mail server, the next step is to make sure it can receive and process +incoming emails. This task is handled by Postfix, which communicates using the SMTP protocol. + +Postfix knows if an email address is valid by checking for… + +- Virtual Domains (am I responsible for this domain?) +- Virtual Aliases (do I have to redirect this address to another address?) +- Virtual Mailboxes (do I have a valid mailbox to store the email to?) + +### Virtual Domains + +There are different ways for Postfix to get that information. From text files, LDAP, MongoDB or PostgreSQL. Or via +MariaDB – which is what we will use. But whatever kind of data source you configure, Postfix needs the information as a +_mapping_. Consider it as a _question_ and an _answer_. + +- Question: is `example.org` one of our virtual domains? +- Answer: yes + +If the information is **not** available you just get no answer: + +- Question: is `example.net` one of our virtual domains? +- Answer: (no answer) + +So Postfix hast to ask MariaDB that question: + +```sql +SELECT "yes" FROM virtual_domains WHERE name='example.net' +``` + +Run the following code in your shell to create a configuration file creating that mapping: + +```sh +cat > /etc/postfix/virtual-mailbox-domains.cf << EOF +user = mailserver +password = SECOND-PASSWORD-HERE +hosts = 127.0.0.1 +dbname = mailserver +query = SELECT 1 FROM virtual_domains WHERE name='%s' +EOF +``` + +This has created a configuration file called `/etc/postfix/virtual-mailbox-domains.cf`. The `user`, `password`, `hosts` +and `dbname` definitions tell Postfix how to connect to the database. And the `query` asks the _question_ if a certain +domain is present in the database table `virtual_domains`. Using `SELECT 1` we return just the number 1 if such an entry +was found. In fact it does not matter what we return. Any _answer_ is fine. + +Don't forget to replace the `SECOND-PASSWORD-HERE` by your own password for the `mailserver` user. + +### Virtual Aliases + +Now let's deal with aliases. As shown earlier an alias redirects an email to another email address. So the _question_ +and _answer_ game goes like this: + +- Question: is there an alias for `jack@example.org`? +- Answer: `john@example.org` + +Postfix would then check if there are further aliases: + +- Question: is there an alias for `john@example.org`? +- Answer: (no answer) + +Apparently, there aren't any. So the email will go to `john@example.org`. + +Run this code to create the appropriate mapping file: + +```sh +cat > /etc/postfix/virtual-alias-maps.cf << EOF +user = mailserver +password = SECOND-PASSWORD-HERE +hosts = 127.0.0.1 +dbname = mailserver +query = SELECT destination FROM virtual_aliases WHERE source='%s' +EOF +``` + +The query now gets all the `destination` email addresses from the database for a certain `source` email address. + +### Virtual Mailboxes + +The last mapping we need is a query to find valid mailboxes. Without further ado: + +```sh +cat > /etc/postfix/virtual-mailbox-maps.cf << EOF +user = mailserver +password = SECOND-PASSWORD-HERE +hosts = 127.0.0.1 +dbname = mailserver +query = SELECT 1 FROM virtual_mailboxes WHERE email='%s' +EOF +``` + +Just the same story as with virtual domains. The database returns `1` if there is a `virtual_mailboxes` record matching +that specific email address. + +Actually the _answer_ is usually not `1` but the path to the mailbox on disk. But that applies only if Postfix would be +saving the email. In our setup the email will be passed on to Dovecot in a later step. Dovecot will then handle the +files on disk. Postfix just has to know is whether a mailbox exists. And that's why any _answer_ is sufficient here. + +### Tell Postfix + +You have created the config files for the three mappings. Now you just need to tell Postfix to use them: + +```sh +postconf virtual_mailbox_domains=mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf +postconf virtual_mailbox_maps=mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf +postconf virtual_alias_maps=mysql:/etc/postfix/mysql-virtual-alias-maps.cf + +chown root:postfix /etc/postfix/*.cf +chmod o= /etc/postfix/*.cf +``` + +`postconf` is a command that changes configuration in `/etc/postfix/main.cf` and applies them instantly. You don't have +to restart Postfix. + +The last two lines set the owner of the config files (_user=root, group=postfix_) and make sure that _others_ have no +access. After all a database password is found in these files. + +### Test it + +Give the mappings a quick test using the `postmap -q` command (_q_ stands for _query_): + +```sh +postmap -q example.org mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf +postmap -q jack@example.org mysql:/etc/postfix/mysql-virtual-alias-maps.cf +postmap -q john@example.org mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf +``` + +These three commands use the three mapping files (`*.cf`) to query your three database tables. The result should show: + +``` +1 +john@example.org +1 +``` + +If you get anything else, please check those three config files. Perhaps the database password is wrong?