I received the notification about your answers only right now and have not checked manually before... So I also have a huge delay in my answer...

First of all: Thanks for your quick replies and your help!

I solved the problem a few days after my post by googling and trying other things -- and ended up in digging deeper into the Postfix configuration. To be honest: I haven't even documented what I did. At the end (after a few days of trying and trying and trying...) I was just happy everything worked. As far as I remember I configured the Postfix Server in a way that it sends the mails over another ("well configured") SMTP Server. It's probably not a very clever and clean solution, but it works...

And yes, TKL v14 IS indeed very different from previous versions, which were "a breeze" even for a complete linux newbie like me. It seems that security (and I totally agree that this is a very, very important issue...) takes it's toll...

With this: Thanks again!

Chris

As I  already said: I don't remember all the steps I made to get it to work...

But if you take all the information here, a couple of hours time and Google as your friend, hopefully you get it to work as well...

I looked it up and as far as I can remember and find out from history I can reproduce at least the following steps (don't remember the right order...):

• Installed the following: dovecot (apt-get install dovecot-imapd dovecot-pop3d)
• Installed  the following:  apt-get install libsasl2-modules-otp libsasl2-modules-ldap libsasl2-modules-sql libsasl2-modules-gssapi-mit libsasl2-modules-gssapi-heimdal
• Created file:   nano /etc/postfix/sasl_passwd  ->  [mailserver.otherdomain.tld]:587 user:password
• Done the following:  postmap /etc/postfix/sasl_passwd

and my /etc/postfix/main.cf looks like this:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = 123.456.789.111.static.anydomain.tld
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = name.domain.tld
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = localdomain, localhost, localhost.localdomain, localhost, name.domain.tld
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
myorigin = name.domain.tld
inet_interfaces = all
smtp_generic_maps = hash:/etc/postfix/generic

# specify SMTP relay host
relayhost = [mailserver.otherdomain.tld]:587

# enable SASL authentication
smtp_sasl_auth_enable = yes
# disallow methods that allow anonymous authentication.
smtp_sasl_security_options = noanonymous
# where to find sasl_passwd
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
# Enable STARTTLS encryption
smtp_use_tls = yes
# where to find CA certificates
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

smtpd_sasl_type = dovecot

# Can be an absolute path, or relative to $queue_directory
# Debian/Ubuntu users: Postfix is setup by default to run chrooted, so it is best to leave it as-is below
smtpd_sasl_path = private/auth