Temporary MTA failure issue

[Alex]

Hi,

I have a fedora15 x86_64 kvm box with amavisd-new-2.6.6 and
postfix-2.8.7 that has been running well for months. For some reason
this morning, I'm receiving errors involving "Temporary MTA Failure on
relaying"

May  8 13:48:19 portal amavis[18551]: (18551-05) (!)rw_loop: leaving
rw loop, no progress, last event (select) 35.035 s ago
May  8 13:48:19 portal amavis[18551]: (18551-05) mail_via_smtp:
session failed: Negative greeting:  at (eval 89) line 596.

May  8 13:48:19 portal amavis[18551]: (18551-05) (!)FWD via SMTP:
<ESC1109953629481_1102890108977_1489_r20 at in.constantcontact.com> ->
<jeff at example.com>, 451 4.5.0 From MTA([127.0.0.1]:10025) during
fwd-connect (Negative greeting:  at (eval 89) line 596.): id=18551-05

May  8 13:48:19 portal amavis[18551]: (18551-05) Blocked MTA-BLOCKED,
[208.XXX.YYY.130] [208.XXX.YYY.130]
<ESC1109953629481_1102890108977_1489_r20 at in.constantcontact.com> ->
<jeff at example.com>, Message-ID:
<1109953629481.1102890108977.1489.1.26134585 at scheduler.constantcontact.com>,
mail_id: AjV8a1Dm8VmS, Hits: -6.322, size: 31309,
dkim_id=@auth.ccsend.com, 55712 ms

May  8 13:48:19 portal postfix/smtp[20131]: 5F5251615AE:
to=<jeff at example.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=118,
delays=0.66/0.06/61/56, dsn=4.5.0, status=deferred (host
127.0.0.1[127.0.0.1] said: 451 4.5.0 id=18551-05 - Temporary MTA
failure on relaying, From MTA([127.0.0.1]:10025) during fwd-connect
(Negative greeting:  at (eval 89) line 596.): id=18551-05 (in reply to
end of DATA command))

I've googled a bit for this, and most questions are either unanswered,
or involve upgrading to a new version that was released years ago.

This has happened several times, resulting in quite a few messages
being deferred. After some time, they apparently clear themselves
without having to restart postfix or amavisd, but I'd like to know why
this is happening.

Thanks for any ideas.
Alex