we are on holidais here

please visit www.microsoft.com

There's more than one place such a function could be.  One is one the
mail server you're using, and Windows Mail does not control it, so log
on using webmail and look for it there.

In Windows Mail, click Tools, then Options, then Receipts.  If there
is a blue dot in the circle before Always send a read receipt, click on
the circle before one of the other two options in this section, then
Apply.  Click on OK.

Click on Tools, then Message Rules, then Mail.  Click on each of
the rules there, and examine the rules to see if they include Reply
with message.  If so, click on Remove before going on to the
next rule.  After the last rule, click on OK.

Note that your function also tells spammers sending to addresses
they have guessed that your address actually works, so they may
use it as a reason to send spam more often, if they actually used a
working return address on the spam (spammers often don't).

Was that possibly something offered on your ISP's webmail site?  The other
way this could have been done is with a message rule - one of the actions
available for message rules is "Reply with a message".

Hal