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I am trying to set up an email server on an Arch Linux VPS using postfix and dovecot. I'm using plain unix password authentication, in which dovecot handles SASL authentication for postfix. For the purpose of this discussion, let's say my domain is at mydomain.com.

Regardless of how I vary the settings that I discuss below, receiving mail works fine.

With the default postfix settings for mynetworks and relay_domains, I thought that my postfix-dovecot-SASL set up would just enable authenticated senders (= unix users who are part of the mail group) to send emails. But when I try to send a test email to a gmail account, I get the error

550 5.1.1 <user@gmail.com>: Recipient address rejected: outside mail is not deliverable

To try to see why I'm not able to send, I started experimenting with the relay_domains setting. Putting

relay_domains = mydomain.com, gmail.com

I can successfully send a test email to my gmail account. However if I put

relay_domains = *

the test email doesn't make it through, but if I put

relay_domains = *, mydomain.com, gmail.com

then the test email does make it through. I know that in the end I don't want to touch the relay_domains setting, and certainly not to set it to *, but I find it thoroughly weird that the * setting, which is meant to be the most permissive, is being completely ignored.

Can anyone give me a clue what's going on here, or suggest what else I should focus on to figure out my email sending problems?

EDIT: here are some more configuration details.

Some settings in postfix main.cf:

compatibility_level = 3.9

mail_owner = postfix


myhostname = mail.mydomain.com
mydomain = mydomain.com
myorigin = $myhostname
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
unknown_local_recipient_reject_code = 550
mynetworks_style = host
default_transport = error: outside mail is not deliverable
home_mailbox = Mail/Inbox/


inet_interfaces = all
inet_protocols = all


SMTP security settings


smtp_tls_security_level = may
smtp_header_checks = regexp:/etc/postfix/smtp_header_checks


smtpd_use_tls = yes
smtpd_tls_cert_file = /path/to/cert.pem
smtpd_tls_key_file = /path/to/key.pem
smtpd_tls_security_level = may


added for SPF


smtpd_recipient_restrictions =
     permit_sasl_authenticated
     permit_mynetworks
     reject_unauth_destination
     check_policy_service unix:private/policy-spf


added for SRS


sender_canonical_maps = socketmap:unix:srs:forward
sender_canonical_classes = envelope_sender
recipient_canonical_maps = socketmap:unix:srs:reverse
recipient_canonical_classes = envelope_recipient, header_recipient

postfix master.cf:

smtp      inet  n       -       n       -       -       smtpd
submission inet n       -       n       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_sasl_type=dovecot
  -o smtpd_sasl_path=private/auth
  -o smtpd_sasl_security_options=noanonymous
  -o smtpd_sasl_local_domain=$myhostname
  -o smtpd_tls_auth_only=yes
  -o smtpd_reject_unlisted_recipient=no
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
  -o smtpd_relay_restrictions=
  -o smtpd_recipient_restrictions =
         reject_non_fqdn_recipient
         reject_unknown_recipient_domain
         permit_sasl_authenticated
         reject
  -o milter_macro_daemon_name=ORIGINATING

pickup    unix  n       -       n       60      1       pickup
cleanup   unix  n       -       n       -       0       cleanup
... etc ...
smtp      unix  -       -       n       -       -       smtp
relay     unix  -       -       n       -       -       smtp
        -o syslog_name=postfix/$service_name
showq     unix  n       -       n       -       -       showq
... etc ...
postlog   unix-dgram n  -       n       -       1       postlogd
policy-spf  unix  -       n       n       -       0       spawn user=nobody argv=/usr/bin/policyd-spf
srsd  unix  -       n       n       -       0       spawn
    user=postsrsd
    argv=/usr/bin/postsrsd -c /etc/postsrsd/postsrsd.conf

Some dovecot settings:

protocols = imap lmtp
auth_mechanisms = plain login

service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
  user = root
}
Mark
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