Horde and unrouteable domains

[dafut]

I have a user on a server that cannot send email from horde--to anywhere. All emails bounce with: "unrouteable domain" response.

User can send through server with email client, like Thunderbird. User receives email to server just fine. User is on reseller account; only user of many that's complaining about this problem. Any thoughts?

Thanks.

[dafut]

I've now got a report on the same server from a SquirrelMail user.

Here's the error:
--
2007-02-01 07:26:32 1HCb1M-0003vW-0w failed to expand condition "${perl{checkspam}}" for literal router: Gid 32150 is not permitted to relay mail at /etc/exim.pl line 365.

2007-02-01 07:26:32 1HCb1M-0003vW-0w ** user@domain.com R=fail_remote_domains: unrouteable mail domain "domain.com"

Looks like it's related to eximmailtrap.