Sendmail Error Message Lost input channel from to MTA after rcpt
Jun 18 10:40:12 MailServer sendmail: r5S59J7h017012: lost input channel from mail.domain.com [x.x.x.x] to MTA after rcpt
Jun 18 10:40:12 MailServer sendmail: r5S59J7h017012: from=, size=0, class=0, nrcpts=1, proto=SMTP, daemon=MTA, relay=mail.domain.com [x.x.x.x]
By adding the IP address or domain names of the rejected mail servers in the Access map, you can ignore this error message.
By disabling the delay check and DNSBL feature in sendmail.mc file you can ignore this error message.
FEATURE(dnsbl, `relays.ordb.org’, `Rejected – see http://ordb.org/’)dnl
FEATURE(dnsbl, `list.dsbl.org’, `Rejected – see http://dsbl.org/’)dnl
FEATURE(dnsbl, `relays.visi.com’, `Rejected – see http://relays.visi.com/’)dnl
FEATURE(dnsbl, `bl.spamcop.net’, `Rejected – see http://bl.spamcop.net/’)dnl
Delay All Check
By using FEATURE(`delay_checks’) the rulesets check_mail and check_relay will not be called when a client connects or issues a MAIL command, respectively. Instead, those rulesets will be called by the check_rcpt ruleset; they will be skipped if a sender has been authenticated using a “trusted” mechanism, i.e., one that is defined via TRUST_AUTH_MECH(). If check_mail returns an error then the RCPT TO command will be rejected with that error. If it returns some other result starting with $# then check_relay will be skipped. If the sender address (or a part of it) is listed in the access map and it has a RHS of OK or RELAY, then check_relay will be skipped.
This has an interesting side effect: if your domain is my.domain and you have
in the access map, then any e-mail with a sender address of will not be rejected by check_relay even though it would match the hostname or IP address. This allows spammers to get around DNS based blacklist by faking the sender address. To avoid this problem you have to use tagged entries:
For more info read this