[TYPO3-english] Powermail dynamic recipient

[N3]

Hello,

I am experiencing trouble with Powermail and dynamic recipients. I have a
Powermail form with a field named recipient. It is a drop-down box, the
values are as follows

Test|1
More Test|2

Its UID is 5.

I would like this drop-down to be used by my visitors to choose the
recipient of their e-mail. Therefore I added the following to the
typoscript:

plugin.tx_powermail_pi1.email.recipient_mail {
email_query = TEXT
email_query.value = SELECT email FROM fe_users WHERE
find_in_set(###UID5###,usergroup) > 0 AND hidden = 0 AND deleted = 0
}

But this ends in an error by TYPO3:
Oops, an error occured!
Address in mailbox given [] does not comply with RFC 2822, 3.6.2.

Since Powermail usually works when I give it a static e-mail address I don't
think this is a problem with the mailing engine but rather that no correct
e-mail addresses is selected by my query. I have double checked the user
group ID, it's correct.

I tried putting the query into my main TS and into the page TS. no result on
either end.

Does anyone out there have this working with Powermail?

I am using TYPO3 4.5.4 and Powermail 1.6.4.

Thank you very much
Jan