spf1.supportboxmailer.cz has no MX records.
Question and response
Question
dig spf1.supportboxmailer.cz. MX
Answer
The response has no answer records.
Authority
supportboxmailer.cz. 900 SOA ns.web4u.cz. admin.web4u.cz. 2025012406 14400 3600 604800 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0