Messages bypass SPF filter. The following error is shown in
CONFIG_TEXT: /usr/lib64/plesk-9.0/psa-pc-remote: Unable to get sender domain by sender mailname
spf filter: Error code: (2) Could not find a valid SPF record
spf filter: Failed to query MAIL-FROM: No DNS data for 'mta.example.com'.
Not all SPF settings were configured.
Check the following conditions, for which SPF filter blocks messages:
SPF record for the sender domain is correctly configured:
CONFIG_TEXT: example.com TXT "v=spf1 a:domain.tld mx -all"
SPF protection is switched on and configured on the destination server ( Tools & Settings > Server-Wide Mail Settings ):
CONFIG_TEXT: SPF local rules: include:spf.trusted-forwarder.org
SPF guess rules: v=spf1 a/24 mx/24 ptr
Detailed information about SPF record syntax is available at Openspf.org