TalkTalk (TT) have recently had problems with the email Auto-Forward facility, in fact it was more than a problem - it stopped working altogether! In my case I used Auto-forward to pass incoming email through my hosting company's spam filter (www.spamexperts.com aka spamfiltering), this process filtered out more junk than TT's, so added an extra line of defence.
Since Auto-Forward has been "fixed" spamfiltering hasn't quaranteened any messages that would have been quaranteened before the "fix" - so I've done some research. My findings may be of interest to others.
Consider this:-
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Header extract BEFORE Auto-Forward problems:-
Message-ID: <8060770e-a6e0-4f67-ab0e-f6d3e3a90482@xtnvmta153.xt.local>
Content-Type: multipart/alternative;
boundary="Nog5Xw40seyh=_?:"
Received-SPF: fail (antispam2.spamfiltering.com: domain of
bounce.s4.exacttarget.com does not designate 62.24.202.74 as permittedsender)
client-ip=62.24.202.74;
envelope-from=bounce-117807_HTML-250381833-812534-1303367-373@bounce.s4.exacttarget.com;
helo=out.ipsmtp2nec.opaltelecom.net;
X-SPF-Result: antispam2.spamfiltering.com: domain of bounce.s4.exacttarget.com
does not designate 62.24.202.74 as permitted sender
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Header extract AFTER Auto-Forward problems:-
Message-ID: <60ffb0f8-a797-46e9-8022-4046b6f64fdf@xtnvmta101.xt.local>
Content-Type: multipart/alternative;
boundary="rrhsjx2a0Gyo=_?:"
Received-SPF: pass (antispam2.spamfiltering.com: domain of
tiscali.co.uk designates 62.24.202.74 as permitted sender) client-ip=62.24.202.74;
envelope-from=my.mum@tiscali.co.uk; helo=out.ipsmtp2nec.opaltelecom.net;
X-SPF-Result: antispam2.spamfiltering.com: domain of tiscali.co.uk
designates 62.24.202.74 as permitted sender
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CONCLUSION
It would appear that before the TT Auto-Forward problems, the forwarded email appeared to originate from bounce.s4.exacttarget.com at IP address 62.24.202.74 so spamfiltering says "does not designate 62.24.202.74 as permitted sender" and proceeds to check email for spam.
After the "fix", the forwarded email appears to originate from tiscali.co.uk at IP address 62.24.202.74 so spamfiltering says "tiscali.co.uk designates 62.24.202.74 as permitted sender" and therefore passes email through without further checks.
This would explain why my spam filtering is behaving differently since TT had their problems! It would also seem that this extra line of defence might now be redundant.
TalkTalk tried to imply that there was nothing wrong with Auto-Forward ("it's an issue with Gmail" and other suggestions), but from the above it appears to me that they've rejigged their forwarding smtp server, as can be seen from the above. Whatever they've done, they screwed up - many customers have lost (for ever) many emails.
I'm no smtp expert, so I'd welcome any feedback from anybody more knowledgeable about such things.