if you changed outbound email server, you may be flagged by MS as a spammer, if it is used to your historical outbound ip(s).

check your test account spam folder.
check your test account (other) filter categories (default from MS).

for example, google's recent changes are redirecting email to new 'categories'.
if you can hand-craft outbound email headers, do a few and change your 'From:' email adrs domain to something like [email protected] and see if those show.

check to see if you've had a recent number of unsubscribes. if so, you may also have a recent number of people hitting [spam] button inside their email systems. which you won't know about.

try sending test emails from some of your other email accounts to your test email account. do those work?

is your outbound server also inbound? if so, test some inbound emails from several accounts, including your test account.

are you using a new mail server, or write new code that generates the emails? if so, maybe there's a slight malformed header that MS is choking on, but other email vendors can handle?

just noodling...

bb

do you still have access to your previous hosting provider, where you can test sending an email from your original source?

if you updated your DNS records to point to a new hosting provider (think you mentioned going from Dallas to Canada previously...), then you'll want to update your MX records with both:
a) the company you have your domain purchased through (ie: godaddy)
b) your actual site/smtp hosting company (ie: in canada?)

They both need to be updated. Your hosting company can walk you through the updates. That change can take up to 48 hours. I've done this for a previous client before to get their email working.

(but - with all that said, are you saying email does get received at non-MS email accounts without a problem? If so, need to better isolate just with MS.)

hope that helps,
bb

Would highly recommend that for gmail users, as email may end up going into the new 'category' pages instead of your Inbox.