Phishing Spam

A week ago, my Yahoo email account became inundated with phishing spam mess=
ages.

I accessed the raw messages. Most of the spams had a X-Originating-Ip assig=
ned to Microsoft. So I sent an email message to [email protected] describ=
ing my experience.

In response, I received a message saying:
   =E2=80=9CBased on the information you provided, it appears to have origi=
nated from=20
        an Office 365 or  Exchange Online tenant account.
    To report junk mail from Office 365 tenants, send an email to=20
        [email protected]=20
        and include the junk mail as an attachment.=E2=80=9D

So I did that.=20

For a few days, the torrent seemed to be reducing. But then the stream of t=
rash increased again.

How can I free myself of this plague?

What=E2=80=99s an Office 365 tenant anyhow? Is that a realm where a Microso=
ft customer is in charge, rather than Microsoft itself?

Does somebody know of a contact in Microsoft that can help?

Is there a contact in Yahoo that can help?

Any fruitful lead is appreciated.

Thanks,
jei