No usable MXs when attempting delivery to SMTP server smtp.libero.it

[l-g1thub-245]

Describe the bug

When sending emails to libero.it, maddy tries to resolve an internal server name, which fails:

2026-05-11T22:31:00.083Z client connection close failed {"msg_id":"a5e41aa7","reason":"close tcp4 192.168.0.170:39245-\u003e213.209.1.129:25: use of closed network connection"}
2026-05-11T22:31:00.083Z cannot use MX {"domain":"libero.it","msg_id":"a5e41aa7","reason":"SMTP error 421: smtp-03.iol.local smtp-03.iol.local No reverse DNS [smtp-03.iol.local; LIB_120]","remote_server":"smtp-in.libero.it.","smtp_code":421,"smtp_enchcode":"0.0.0","smtp_msg":"smtp-in.libero.it. said: smtp-03.iol.local smtp-03.iol.local No reverse DNS [smtp-03.iol.local; LIB_120]"}
2026-05-11T22:31:00.083Z submission: RCPT error {"domain":"libero.it","effective_rcpt":"xxxxx.xxxx@libero.it","msg_id":"a5e41aa7","rcpt":"xxxxx.xxxx@libero.it","reason":"SMTP error 421: smtp-03.iol.local smtp-03.iol.local No reverse DNS [smtp-03.iol.local; LIB_120]","remote_server":"smtp-in.libero.it.","smtp_code":451,"smtp_enchcode":"5.4.0","smtp_msg":"No usable MXs, last err: SMTP error 421: smtp-03.iol.local smtp-03.iol.local No reverse DNS [smtp-03.iol.local; LIB_120]","target":"remote"}

Using mxtoolbox.com to simulate the connection to smtp.libero.it, the advertised server name is not public :

Connecting to 213.209.1.144

220 smtp-31.iol.local smtp-31.iol.local ESMTP server ready [234 ms]
EHLO keeper-us-east-1d.mxtoolbox.com
250-smtp-31.iol.local hello [18.209.86.113], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 50000000
250-8BITMIME
250-STARTTLS
250 OK [219 ms]
MAIL FROM:supertool@mxtoolboxsmtpdiag.com

What do you think is wrong?

Attempts to resolve smtp-31.iol.local / smtp-03.iol.local / etc fail

Steps to reproduce

It happens every time an email is sent to libero.it

Log files

Configuration file

target.remote outbound_delivery {

limits {
    # Up to 20 msgs/sec across max. 10 SMTP connections
    # for each recipient domain.
    destination rate 20 1s
    destination concurrency 10
}
mx_auth {
    dnssec
    dane
    mtasts {
        cache fs
        fs_dir mtasts_cache/
    }
    local_policy {
        min_tls_level none
        min_mx_level none
    }
}

}

Environment information

• maddy version: ?
  0.9.4

[foxcpp]

maddy does not try to resolve EHLO hostname provided by the remote MX. However, seems like libero.it MX expects senders to advertise a forward-confirmed rDNS name which is actually a common thing to require. Check if hostname provided in config resolves to the actual IP your server uses and is reachable at and then also check that you have an PTR record on that IP pointing to the same domain.