I'm currently running Release 7.2.2_GA_2852.UBUNTU8 UBUNTU8 NETWORK edition.
I have been experiencing a large amount of
dsn=4.4.2, status=deferred (lost connection with mta7.am0.yahoodns.net[184.108.40.206] while sending end of data -- message may be sent more than once)
dsn=4.4.1, status=deferred (connect to reichleylns.com[220.127.116.11]:25: Connection timed out)
Most of the time it is with a Yahoo / SCBGlobal / AT&T / YMail address.
I believe it is a DNS error but I have verified that the setting are correct. I have reviewed the forum and tried several fixes with no avail.
When I ran the command "host `hostname`" I received the following error
root@mailserver:/# host `hostname`
\$ has address 18.104.22.168
\$ has address 22.214.171.124
Host \$ not found: 3(NXDOMAIN)