[Zope] Sendmail: Problem with string.join

[Steve Smith]

OK, what's wrong with this then?

<dtml-let email_list=dbGetRumourInterest>
<dtml-let followup_list=dbGetFollowups>
<dtml-if email_list>
<dtml-sendmail mailhost="MailHost">
To: <dtml-var expr="_.string.join(email_list,',')">
From: ozrail@bigpond.net.au
etc...

I found the string.join example in an email from Dieter, but when I try this
I get an error: first argument must be a sequence of strings.

When I run the SQL standalone, it returns what looks like a sequence of
strings to me. Any clues out there?

Steve