Simplenews sending mails with empty body/subject

I'm using SimpleNews to sent out a newsletter to subscribed user, and while the mail is going through, when it arrives in the user's mailbox, it has neither a subject nor body text, and in the email headers, I get "X-Amavis-Alert: BAD HEADER MIME error: error: unexpected end of preamble".

Because of the way my server is set up, I'm forced to use smtp to send mail (for which I'm using the PHPMailer module. I also tried the SMTP module and SimpleNews didn't send at all). I'm also using the MimeMail module in order to send html emails. All other emails from my site come through fine. It's only when I'm sending through SimpleNews that I run into this problem. Any help would be appreciated. I'm at a loss.

Full headers from the email:
Return-Path:
Received: from mail.illinimedia.com ([unix socket])
by mail.illinimedia.com (Cyrus v2.2.12-OS X 10.4.8) with LMTPA;
Thu, 02 Apr 2009 11:32:09 -0500
X-Sieve: CMU Sieve 2.2
Received: from localhost (localhost [127.0.0.1])
by mail.illinimedia.com (Postfix) with ESMTP id EF1022A9D407;
Thu, 2 Apr 2009 11:32:08 -0500 (CDT)
Received: from mail.illinimedia.com ([127.0.0.1])
by localhost (scooter.internal.illinimedia.com [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id 19139-04; Thu, 2 Apr 2009 11:32:02 -0500 (CDT)
Received: from staging.dailyillini.com (fozzie.illinimedia.com [66.209.200.202])
by mail.illinimedia.com (Postfix) with ESMTP id 80BF72A9D3EA;
Thu, 2 Apr 2009 11:32:00 -0500 (CDT)
Errors-To: no-reply@dailyillini.com
From: "The Daily Illini"
Content-Type: multipart/alternative;
charset=utf-8;
boundary="60a8f99ec94ebf9274c3cac3081edb76"
MIME-Version: 1.0
Content-Transfer-Encoding: 8Bit
X-Mailer: Drupal
Sender: no-reply@dailyillini.com
Reply-To: "The Daily Illini"
Precedence: bulk
List-Unsubscribe:
Message-Id: <20090402163200.80BF72A9D3EA@mail.illinimedia.com>
Date: Thu, 2 Apr 2009 11:32:00 -0500 (CDT)
To: undisclosed-recipients: ;
X-Amavis-Alert: BAD HEADER MIME error: error: unexpected end of preamble
X-Spam-Status: No, hits=0.569 tagged_above=-999 required=4 tests=AWL,
BAYES_00, EMPTY_MESSAGE, MISSING_SUBJECT, TVD_SPACE_RATIO
X-Spam-Level: