Hi Henrik,
yes, the source of the mails is different. The 'good' or plain text mails have:
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
and the 'bad' ones have:
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
but this happens on the xymon server. I see from /var/log/maillog
Apr 30 13:07:40 xymon64 sSMTP[16315]: 354 Start mail input; end with <CRLF>.<CRLF>
Apr 30 13:07:40 xymon64 sSMTP[16315]: Received: by xymon64.domain.com (sSMTP sendmail emulation); Mon, 30 Apr 2012 13:07:40 +0200
Apr 30 13:07:40 xymon64 sSMTP[16315]: From: "xymon Monitor" <user-8fbb006e94d3@xymon.invalid>
Apr 30 13:07:40 xymon64 sSMTP[16315]: Date: Mon, 30 Apr 2012 13:07:40 +0200
Apr 30 13:07:40 xymon64 sSMTP[16315]: To: user-afe02cd6ed72@xymon.invalid
Apr 30 13:07:40 xymon64 sSMTP[16315]: Subject: Xymon server.domain.com:http recovered
Apr 30 13:07:40 xymon64 sSMTP[16315]: User-Agent: Heirloom mailx 12.4 7/29/08
Apr 30 13:07:40 xymon64 sSMTP[16315]: MIME-Version: 1.0
Apr 30 13:07:40 xymon64 sSMTP[16315]: Content-Type: application/octet-stream
Apr 30 13:07:40 xymon64 sSMTP[16315]: Content-Transfer-Encoding: base64
KR
Daniel