[exim] Temporary error not treated as such

I've got a stable installation ov v 4.67 . It's not quite the latest but I
can't see anything relevant in the Changelog.

I just mailed a friend via the local squirrelmail and got an immediate
bounce from what looks like a temporary error.

The second line shows a 421 error from the remote system.

(The extra stuff is my maildrop forwarding a copy to my gmail)

Why is the 421 causing an immediate failure ?

Jon

2008-03-25 17:11:34 1JeCgP-0000A8-SS <= jon@??? U=www-data
P=local S=1468 id=35195.192.168.3.32.1206465093.squirrel@ma
il.jschneider.net
2008-03-25 17:11:34 1JeCgP-0000A8-SS == jan@??? R=dnslookup
T=remote_smtp defer (-44): SMTP error from remote mail server
after RCPT TO:<jan@???>: host mail.xxxxx.com [213.232.100.89]: 421
temporary envelope failure (#4.3.0)
2008-03-25 17:11:34 1JeCgP-0000A8-SS ** jan@???: retry timeout exceeded
2008-03-25 17:11:34 1JeCgQ-0000AH-Qa <= <> R=1JeCgP-0000A8-SS U=mail
P=local S=2421
2008-03-25 17:11:35 1JeCgP-0000A8-SS Completed
2008-03-25 17:11:35 1JeCgR-0000AO-52 <= jms@??? U=jms P=local
S=2650 id=E1JeCgQ-0000AH-Qa@???
2008-03-25 17:11:35 1JeCgQ-0000AH-Qa => |/usr/bin/maildrop
(jms@???) <jon@???> R=userforward T=address_pi
pe
2008-03-25 17:11:35 1JeCgQ-0000AH-Qa Completed
2008-03-25 17:11:37 1JeCgR-0000AO-52 => yyyyy@??? R=dnslookup
T=remote_smtp H=gmail-smtp-in.l.google.com [64.233.183.114]
2008-03-25 17:11:37 1JeCgR-0000AO-52 Completed