Mail delivery is very slow

[Frédéric Médery]

Hello ML users,
setup :
RG 9.0 postfix, mailscanner, spamassassin
it's a SMPT gateway (no local user)
I'm using the transport file (postfix) to route mail to Exchange
with :
netgroupes.ca           smtp:[192.168.168.5]
This server is the first MX of the domain

The delivery is very slow.
Here is a example :
Nov 21 14:38:47 thor postfix/smtpd[6774]: connect from unknown[207.245.51.50]
Nov 21 14:38:47 thor postfix/smtpd[6774]: 845C0BE72: client=unknown[207.245.51.50]
Nov 21 14:38:47 thor postfix/cleanup[6777]: 845C0BE72: message-id=<002d01c3b067$167a4de0$0200000a at SVR.FRE.COM>
Nov 21 14:38:47 thor postfix/nqmgr[6671]: 845C0BE72: from=<Administrator at frecomposites.com>, size=1630, nrcpt=1 (queue active)
Nov 21 14:38:47 thor postfix/smtpd[6774]: disconnect from unknown[207.245.51.50]
Nov 21 14:38:47 thor postfix/nqmgr[6671]: 845C0BE72: to=<fmedery at netgroupes.ca>, relay=none, delay=0, status=deferred (deferred transport)
Nov 21 14:38:49 thor MailScanner[6715]: New Batch: Scanning 1 messages, 1803 bytes
Nov 21 14:38:50 thor MailScanner[6715]: Spam Checks: Starting
Nov 21 14:38:50 thor MailScanner[6715]: Virus and Content Scanning: Starting
Nov 21 14:38:52 thor postfix/nqmgr[6680]: A2F7AAA541: from=<administrator at frecomposites.com>, size=1754, nrcpt=1 (queue active)

Nov 21 14:38:52 thor MailScanner[6715]: Uninfected: Delivered 1 messages

Nov 21 14:40:13 thor postfix/smtp[6791]: A2F7AAA541: to=<fmedery at netgroupes.ca>, relay=192.168.168.5[192.168.168.5], delay=86, status=sent (250 2.6.0  <002d01c3b067$167a4de0$0200000a at SVR.FRE.COM> Queued mail for delivery)


As you can see,
it took 2 min between the last to line.

CPU and mem are very low so it does not seems to be a perf issue.

I double check the mailscanner+postfix installation and everything is
"by the book".

Some advice ?

Thanks !!!