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

# 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:

# 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