Hi,
The forum notification messages don't have date on them. Email messages are required to have a valid date and if they don't a lot of anti spam software will probably reject them. See below extract of my spam filter log:
X-Quarantine-ID: <4eXYluWqGGvL>
X-Virus-Scanned: Debian amavisd-new at li40-130.members.linode.com
X-Amavis-Alert: BAD HEADER SECTION, Missing required header field: "Date"
Ian.