Monitoring external SMTP service

[Christian Bianchi]

Good morning everyone

i want to use monit to check availability of an antispam service
(managed by others) from outside.
for this i added this config to monit:

check host my-name
       with address my.external.host.name
       if failed host my.external.host.name port 25 protocol smtp with
timeout 15 seconds then alert

but it doesn't work.
i keep receiving alert of service down by monit and in the monit log i
read this:

[CET Jan  5 09:38:46] error    : SMTP: error receiving data --
Resource temporarily unavailable
[CET Jan  5 09:38:46] error    : 'my-name' failed protocol test [SMTP]
at INET[my.external.host.name:25] via TCP

note that smtp is up and running (tested from same server using telnet
my.external.host.name 25

any hints?

-- 
Christian Bianchi
eNBilab srl.
via Castellana 45/a int. 4, 33100 Udine
www.enbilab.com
tel +39 0432 906545