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diff --git a/blog/src/a/mail_server_with_postfix.md b/blog/src/a/mail_server_with_postfix.md deleted file mode 100644 index 63bf564..0000000 --- a/blog/src/a/mail_server_with_postfix.md +++ /dev/null @@ -1,517 +0,0 @@ -title: Create a mail server with Postfix, Dovecot, SpamAssassin and OpenDKIM -author: David Luévano -lang: en -summary: How to create mail server using Postfix, Dovecot, SpamAssassin and OpenDKIM. This is a follow up on post about creating a website with Nginx and Certbot. -tags: server - tools - tutorial - english - -The entry is going to be long because it's a *tedious* process. This is also based on [Luke Smith's script](https://github.com/LukeSmithxyz/emailwiz), but adapted to Arch Linux (his script works on debian-based distributions). This entry is mostly so I can record all the notes required while I'm in the process of installing/configuring the mail server on a new VPS of mine; also I'm going to be writing a script that does everything in one go (for Arch Linux), that will be hosted [here](https://git.luevano.xyz/server_scripts.git). - -This configuration works for local users (users that appear in `/etc/passwd`), and does not use any type of SQL Database. And note that most if not all commands executed here are run with root privileges. - -## Prerequisites - -Basically the same as with the [website with Nginx and Certbot](https://blog.luevano.xyz/a/website_with_nginx.html), with the extras: - -- You will need a **CNAME** for "mail" and (optionally) "www.mail", or whatever you want to call the sub-domains (although the [RFC 2181](https://tools.ietf.org/html/rfc2181#section-10.3) states that it NEEDS to be an **A** record, fuck the police). -- An SSL certificate. You can use the SSL certificate obtained following my last post using `certbot` (just create a `mail.conf` and run `certbot --nginx` again). -- Ports 25, 587 (SMTP), 465 (SMTPS), 143 (IMAP) and 993 (IMAPS) open on the firewall. - -## Postfix - -[Postfix](https://wiki.archlinux.org/title/postfix) is a "mail transfer agent" which is the component of the mail server that receives and sends emails via SMTP. - -Install the `postfix` package: - -```sh -pacman -S postfix -``` - -We have two main files to configure (inside `/etc/postfix`): `master.cf` ([master(5)](https://man.archlinux.org/man/master.5)) and `main.cf` ([postconf(5)](https://man.archlinux.org/man/postconf.5)). We're going to edit `main.cf` first either by using the command `postconf -e 'setting'` or by editing the file itself (I prefer to edit the file). - -Note that the default file itself has a lot of comments with description on what each thing does (or you can look up the manual, linked above), I used what Luke's script did plus some other settings that worked for me. - -Now, first locate where your website cert is, mine is at the default location `/etc/letsencrypt/live/`, so my `certdir` is `/etc/letsencrypt/live/luevano.xyz`. Given this information, change `{yourcertdir}` on the corresponding lines. The configuration described below has to be appended in the `main.cf` configuration file. - -Certificates and ciphers to use for authentication and security: - -```apache -smtpd_tls_key_file = {yourcertdir}/privkey.pem -smtpd_tls_cert_file = {yourcertdir}/fullchain.pem -smtpd_use_tls = yes -smtpd_tls_auth_only = yes -smtp_tls_security_level = may -smtp_tls_loglevel = 1 -smtp_tls_CAfile = {yourcertdir}/cert.pem -smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 -smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 -smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 -smtp_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 -tls_preempt_cipherlist = yes -smtpd_tls_exclude_ciphers = aNULL, LOW, EXP, MEDIUM, ADH, AECDH, MD5, - DSS, ECDSA, CAMELLIA128, 3DES, CAMELLIA256, - RSA+AES, eNULL - -smtp_tls_CApath = /etc/ssl/certs -smtpd_tls_CApath = /etc/ssl/certs - -smtpd_relay_restrictions = permit_sasl_authenticated, permit_mynetworks, defer_unauth_destination -``` - -Also, for the *connection* with `dovecot`, append the next few lines (telling postfix that `dovecot` will use user/password for authentication): - -```apache -smtpd_sasl_auth_enable = yes -smtpd_sasl_type = dovecot -smtpd_sasl_path = private/auth -smtpd_sasl_security_options = noanonymous, noplaintext -smtpd_sasl_tls_security_options = noanonymous -``` - -Specify the mailbox home (this is going to be a directory inside your user's home containing the actual mail files): - -```apache -home_mailbox = Mail/Inbox/ -``` - -Pre-configuration to work seamlessly with `dovecot` and `opendkim`: - -```apache -myhostname = {yourdomainname} -mydomain = localdomain -mydestination = $myhostname, localhost.$mydomain, localhost - -milter_default_action = accept -milter_protocol = 6 -smtpd_milters = inet:127.0.0.1:8891 -non_smtpd_milters = inet:127.0.0.1:8891 -mailbox_command = /usr/lib/dovecot/deliver -``` - -Where `{yourdomainname}` is `luevano.xyz` in my case, or if you have `localhost` configured to your domain, then use `localhost` for `myhostname` (`myhostname = localhost`). - -Lastly, if you don't want the sender's IP and user agent (application used to send the mail), add the following line: - -```apache -smtp_header_checks = regexp:/etc/postfix/smtp_header_checks -``` - -And create the `/etc/postfix/smtp_header_checks` file with the following content: - -```coffee -/^Received: .*/ IGNORE -/^User-Agent: .*/ IGNORE -``` - -That's it for `main.cf`, now we have to configure `master.cf`. This one is a bit more tricky. - -First look up lines (they're uncommented) `smtp inet n - n - - smtpd`, `smtp unix - - n - - smtp` and `-o syslog_name=postfix/$service_name` and either delete or uncomment them... or just run `sed -i "/^\s*-o/d;/^\s*submission/d;/\s*smtp/d" /etc/postfix/master.cf` as stated in Luke's script. - -Lastly, append the following lines to complete postfix setup and pre-configure for `spamassassin`. - -```txt -smtp unix - - n - - smtp -smtp inet n - y - - smtpd - -o content_filter=spamassassin -submission inet n - y - - smtpd - -o syslog_name=postfix/submission - -o smtpd_tls_security_level=encrypt - -o smtpd_sasl_auth_enable=yes - -o smtpd_tls_auth_only=yes -smtps inet n - y - - smtpd - -o syslog_name=postfix/smtps - -o smtpd_tls_wrappermode=yes - -o smtpd_sasl_auth_enable=yes -spamassassin unix - n n - - pipe - user=spamd argv=/usr/bin/vendor_perl/spamc -f -e /usr/sbin/sendmail -oi -f \${sender} \${recipient} -``` - -Now, I ran into some problems with postfix, one being [smtps: Servname not supported for ai_socktype](https://www.faqforge.com/linux/fix-for-opensuse-error-postfixmaster-fatal-0-0-0-0smtps-servname-not-supported-for-ai_socktype/), to fix it, as *Till* posted in that site, edit `/etc/services` and add: - -```apache -smtps 465/tcp -smtps 465/udp -``` - -Before starting the `postfix` service, you need to run `newaliases` first, but you can do a bit of configuration beforehand editing the file `/etc/postfix/aliases`. I only change the `root: you` line (where `you` is the account that will be receiving "root" mail). After you're done, run: - -```sh -postalias /etc/postfix/aliases -newaliases -``` - -At this point you're done configuring `postfix` and you can already start/enable the `postfix` service: - -```sh -systemctl start postfix.service -systemctl enable postfix.service -``` - -## Dovecot - -[Dovecot](https://wiki.archlinux.org/title/Dovecot) is an IMAP and POP3 server, which is what lets an email application retrieve the mail. - -Install the `dovecot` and `pigeonhole` (sieve for `dovecot`) packages: - -```sh -pacman -S dovecot pigeonhole -``` - -On arch, by default, there is no `/etc/dovecot` directory with default configurations set in place, but the package does provide the example configuration files. Create the `dovecot` directory under `/etc` and, optionally, copy the `dovecot.conf` file and `conf.d` directory under the just created `dovecot` directory: - -```sh -mkdir /etc/dovecot -cp /usr/share/doc/dovecot/example-config/dovecot.conf /etc/dovecot/dovecot.conf -cp -r /usr/share/doc/dovecot/example-config/conf.d /etc/dovecot -``` - -As Luke stated, `dovecot` comes with a lot of "modules" (under `/etc/dovecot/conf.d/` if you copied that folder) for all sorts of configurations that you can include, but I do as he does and just edit/create the whole `dovecot.conf` file; although, I would like to check each of the separate configuration files `dovecot` provides I think the options Luke provides are more than good enough. - -I'm working with an empty `dovecot.conf` file. Add the following lines for SSL and login configuration (also replace `{yourcertdir}` with the same certificate directory described in the Postfix section above, note that the `<` is required): - -```apache -ssl = required -ssl_cert = <{yourcertdir}/fullchain.pem -ssl_key = <{yourcertdir}/privkey.pem -ssl_min_protocol = TLSv1.2 -ssl_cipher_list = ALL:!RSA:!CAMELLIA:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SHA1:!SHA256:!SHA384:!LOW@STRENGTH -ssl_prefer_server_ciphers = yes -ssl_dh = </etc/dovecot/dh.pem - -auth_mechanisms = plain login -auth_username_format = %n -protocols = $protocols imap -``` - -You may notice we specify a file we don't have under `/etc/dovecot`: `dh.pem`. We need to create it with `openssl` (you should already have it installed if you've been following this entry and the one for `nginx`). Just run (might take a few minutes): - -```sh -openssl dhparam -out /etc/dovecot/dh.pem 4096 -``` - -After that, the next lines define what a "valid user is" (really just sets the database for users and passwords to be the local users with their password): - -```apache -userdb { - driver = passwd -} - -passdb { - driver = pam -} -``` - -Next, comes the mail directory structure (has to match the one described in the Postfix section). Here, the `LAYOUT` option is important so the boxes are `.Sent` instead of `Sent`. Add the next lines (plus any you like): - -```apache -mail_location = maildir:~/Mail:INBOX=~/Mail/Inbox:LAYOUT=fs -namespace inbox { - inbox = yes - - mailbox Drafts { - special_use = \Drafts - auto = subscribe - } - - mailbox Junk { - special_use = \Junk - auto = subscribe - autoexpunge = 30d - } - - mailbox Sent { - special_use = \Sent - auto = subscribe - } - - mailbox Trash { - special_use = \Trash - } - - mailbox Archive { - special_use = \Archive - } -} -``` - -Also include this so Postfix can use Dovecot's authentication system: - -```apache -service auth { - unix_listener /var/spool/postfix/private/auth { - mode = 0660 - user = postfix - group = postfix - } -} -``` - -Lastly (for Dovecot at least), the plugin configuration for `sieve` (`pigeonhole`): - -```apache -protocol lda { - mail_plugins = $mail_plugins sieve -} - -protocol lmtp { - mail_plugins = $mail_plugins sieve -} - -plugin { - sieve = ~/.dovecot.sieve - sieve_default = /var/lib/dovecot/sieve/default.sieve - sieve_dir = ~/.sieve - sieve_global_dir = /var/lib/dovecot/sieve/ -``` - -Where `/var/lib/dovecot/sieve/default.sieve` doesn't exist yet. Create the folders: - -```sh -mkdir -p /var/lib/dovecot/sieve -``` - -And create the file `default.sieve` inside that just created folder with the content: - -```nginx -require ["fileinto", "mailbox"]; -if header :contains "X-Spam-Flag" "YES" { - fileinto "Junk"; -} -``` - -Now, if you don't have a `vmail` (virtual mail) user, create one and change the ownership of the `/var/lib/dovecot` directory to this user: - -```sh -grep -q "^vmail:" /etc/passwd || useradd -m vmail -s /usr/bin/nologin -chown -R vmail:vmail /var/lib/dovecot -``` - -Note that I also changed the shell for `vmail` to be `/usr/bin/nologin`. After that, to compile the configuration file run: - -```sh -sievec /var/lib/dovecot/sieve/default.sieve -``` - -A `default.svbin` file will be created next to `default.sieve`. - -Next, add the following lines to `/etc/pam.d/dovecot` if not already present (shouldn't be there if you've been following these notes): - -```txt -auth required pam_unix.so nullok -account required pam_unix.so -``` - -That's it for Dovecot, at this point you can start/enable the `dovecot` service: - -```sh -systemctl start dovecot.service -systemctl enable dovecot.service -``` - -## OpenDKIM - -[OpenDKIM](https://wiki.archlinux.org/title/OpenDKIM) is needed so services like G\*\*gle (we don't mention that name here \[\[\[this is a meme\]\]\]) don't throw the mail to the trash. DKIM stands for "DomainKeys Identified Mail". - -Install the `opendkim` package: - -```sh -pacman -S opendkim -``` - -Generate the keys for your domain: - -```sh -opendkim-genkey -D /etc/opendkim -d {yourdomain} -s {yoursubdomain} -r -b 2048 -``` - -Where you need to change `{yourdomain}` and `{yoursubdomain}` (doesn't really need to be the sub-domain, could be anything that describes your key) accordingly, for me it's `luevano.xyz` and `mail`, respectively. After that, we need to create some files inside the `/etc/opendkim` directory. First, create the file `KeyTable` with the content: - -```txt -{yoursubdomain}._domainkey.{yourdomain} {yourdomain}:{yoursubdomain}:/etc/opendkim/{yoursubdomain}.private -``` - -So, for me it would be: - -```txt -mail._domainkey.luevano.xyz luevano.xyz:mail:/etc/opendkim/mail.private -``` - -Next, create the file `SigningTable` with the content: - -```txt -*@{yourdomain} {yoursubdomain}._domainkey.{yourdomain} -``` - -Again, for me it would be: - -```txt -*@luevano.xyz mail._domainkey.luevano.xyz -``` - -And, lastly create the file `TrustedHosts` with the content: - -```txt -127.0.0.1 -::1 -10.1.0.0/16 -1.2.3.4/24 -localhost -{yourserverip} -... -``` - -And more, make sure to include your server IP and something like `subdomain.domainname`. - -Next, edit `/etc/opendkim/opendkim.conf` to reflect the changes (or rather, addition) of these files, as well as some other configuration. You can look up the example configuration file located at `/usr/share/doc/opendkim/opendkim.conf.sample`, but I'm creating a blank one with the contents: - -```apache -Domain {yourdomain} -Selector {yoursubdomain} - -Syslog Yes -UserID opendkim - -KeyFile /etc/opendkim/{yoursubdomain}.private -Socket inet:8891@localhost -``` - -Now, change the permissions for all the files inside `/etc/opendkim`: - -```sh -chown -R root:opendkim /etc/opendkim -chmod g+r /etc/postfix/dkim/* -``` - -I'm using `root:opendkim` so `opendkim` doesn't complain about the `{yoursubdomani}.private` being insecure (you can change that by using the option `RequireSafeKeys False` in the `opendkim.conf` file, as stated [here](http://lists.opendkim.org/archive/opendkim/users/2014/12/3331.html)). - -That's it for the general configuration, but you could go more in depth and be more secure with some extra configuration. - -Now, just start/enable the `opendkim` service: - -```sh -systemctl start opendkim.service -systemctl enable opendkim.service -``` - -And don't forget to add the following **TXT** records on your domain registrar (these examples are for Epik): - -1. *DKIM* entry: look up your `{yoursubdomain}.txt` file, it should look something like: - -```txt -{yoursubdomain}._domainkey IN TXT ( "v=DKIM1; k=rsa; s=email; " - "p=..." - "..." ) ; ----- DKIM key mail for {yourdomain} -``` - -In the TXT record you will place `{yoursubdomain}._domainkey` as the "Host" and `"v=DKIM1; k=rsa; s=email; " "p=..." "..."` in the "TXT Value" (replace the dots with the actual value you see in your file). - -2. *DMARC* entry: just `_dmarc.{yourdomain}` as the "Host" and `"v=DMARC1; p=reject; rua=mailto:dmarc@{yourdomain}; fo=1"` as the "TXT Value". - -3. *SPF* entry: just `@` as the "Host" and `"v=spf1 mx a:{yoursubdomain}.{yourdomain} - all"` as the "TXT Value". - -And at this point you could test your mail for spoofing and more. - -## SpamAssassin - -[SpamAssassin](https://wiki.archlinux.org/title/SpamAssassin) is just *a mail filter to identify spam*. - -Install the `spamassassin` package (which will install a bunch of ugly `perl` packages...): - -```sh -pacman -S spamassassin -``` - -For some reason, the permissions on all `spamassassin` stuff are all over the place. First, change owner of the executables, and directories: - -```sh -chown spamd:spamd /usr/bin/vendor_perl/sa-* -chown spamd:spamd /usr/bin/vendor_perl/spam* -chwown -R spamd:spamd /etc/mail/spamassassin -``` - -Then, you can edit `local.cf` (located in `/etc/mail/spamassassin`) to fit your needs (I only uncommented the `rewrite_header Subject ...` line). And then you can run the following command to update the patterns and compile them: - -```sh -sudo -u spamd sa-update -sudo -u spamd sa-compile -``` - -And since this should be run periodically, create the service `spamassassin-update.service` under `/etc/systemd/system` with the following content: - -```ini -[Unit] -Description=SpamAssassin housekeeping -After=network.target - -[Service] -User=spamd -Group=spamd -Type=oneshot - -ExecStart=/usr/bin/vendor_perl/sa-update --allowplugins -SuccessExitStatus=1 -ExecStart=/usr/bin/vendor_perl/sa-compile -ExecStart=/usr/bin/systemctl -q --no-block try-restart spamassassin.service -``` - -And you could also execute `sa-learn` to train `spamassassin`'s bayes filter, but this works for me. Then create the timer `spamassassin-update.timer` under the same directory, with the content: - -```ini -[Unit] -Description=SpamAssassin housekeeping - -[Timer] -OnCalendar=daily -Persistent=true - -[Install] -WantedBy=timers.target -``` - -You can now start/enable the `spamassassin-update` timer: - -```sh -systemctl start spamassassin-update.timer -systemctl enable spamassassin-update.timer -``` - -Next, you may want to edit the `spamassassin` service before starting and enabling it, because by default, it could [spawn a lot of "childs"](https://rimuhosting.com/howto/memory.jsp) eating a lot of resources and you really only need one child. Append `--max-children=1` to the line `ExecStart=...` in `/usr/bin/systemd/system/spamassassin.service`: - -```ini -... -ExecStart=/usr/bin/vendor_perl/spamd -x -u spamd -g spamd --listen=/run/spamd/spamd.sock --listen=localhost --max-children=1 -... -``` - -Finally, start and enable the `spamassassin` service: - -```sh -systemctl start spamassassin.service -systemctl enable spamassassin.service -``` - -## Wrapping up - -We should have a working mail server by now. Before continuing check your journal logs (`journalctl -xe --unit={unit}`, where `{unit}` could be `spamassassin.service` for example) to see if there was any error whatsoever and try to debug it, it should be a typo somewhere (the logs are generally really descriptive) because all the settings and steps detailed here just (literally just finished doing everything on a new server as of the writing of this text) worked *(((it just werks on my machine)))*. - -Now, to actually use the mail service: first of all, you need a *normal* account (don't use root) that belongs to the `mail` group (`gpasswd -a user group` to add a user `user` to group `group`) and that has a password. - -Next, to actually login into a mail app/program/whateveryouwanttocallit, you will use the following settings, at least for `thunderdbird`(I tested in windows default mail app and you don't need a lot of settings): - -- \* server: subdomain.domain (mail.luevano.xyz in my case) -- **SMTP** port: 587 -- **SMTPS** port: 465 (I use this one) -- **IMAP** port: 143 -- **IMAPS** port: 993 (again, I use this one) -- Connection/security: SSL/TLS -- Authentication method: Normal password -- Username: just your `user`, not the whole email (`david` in my case) -- Password: your `user` password (as in the password you use to login to the server with that user) - -All that's left to do is test your mail server for spoofing, and to see if everything is setup correctly. Go to [DKIM Test](https://www.appmaildev.com/en/dkim) and follow the instructions (basically click next, and send an email with whatever content to the email that they provide). After you send the email, you should see something like: - - - -Finally, that's actually it for this entry, if you have any problem whatsoever you can [contact me](https://luevano.xyz/contact.html). |