Hi Ralf,
We had the same problem few months back and i remember that was the
action we took to mitigate the issue. I will state our dovecot `s
submission proxy relevant config and hope that it will help.
```
auth_mechanisms = plain login
submission_max_mail_size = 30720000
submission_relay_host = smtp_ip
submission_relay_port = 587
submission_relay_trusted = yes
submission_relay_ssl = starttls
submission_relay_ssl_verify = no
submission_client_workarounds = whitespace-before-path
```
Our smtp server is running postfix. We use the following configuration
for postfix`s master.cnf submission(port 587)
```
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
-o smtpd_reject_unlisted_recipient=no
# -o smtpd_client_restrictions=$mua_client_restrictions
# -o smtpd_helo_restrictions=$mua_helo_restrictions
-o smtpd_sender_restrictions=$mua_sender_restrictions
-o smtpd_recipient_restrictions=$mua_recipient_restrictions
-o smtpd_relay_restrictions=$mua_relay_restrictions
-o milter_macro_daemon_name=ORIGINATING
-o smtpd_authorized_xclient_hosts=dovecot_host1_ip,dovecot_host2_ip
-o smtpd_sasl_authenticated_header=no
-o smtpd_sasl_path=smtpd
-o smtpd_sasl_security_options=noanonymous
-o smtpd_sasl_type=cyrus
-o smtpd_sender_login_maps=$mua_sender_login_maps
-o smtpd_tls_ciphers=high
-o smtpd_tls_exclude_ciphers=$mua_exclude_ciphers
-o smtpd_tls_mandatory_ciphers=high
-o smtpd_tls_mandatory_exclude_ciphers=$mua_exclude_ciphers
-o smtpd_tls_mandatory_protocols=$mua_tls_protocols
-o smtpd_tls_protocols=$mua_tls_protocols
-o smtpd_tls_received_header=yes
-o tls_preempt_cipherlist=yes
```
On 22/5/23 16:25, Nikolaos Pyrgiotis wrote:
Have you tried adding the line below to your submision config?
submission_client_workarounds = whitespace-before-path
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