Have you confirmed that email works at all.
I ask because you have migrated to a new host
Like login directly to email in the cpanel and see if emails go out?
Meaning use the same email account that you are using in UBB.
It could be you are blacklisted. or something is not setup correctly
FYI.
if sending to a outlook account It could be just outlook try sending to say a gmail account.
Outlook is very picky on your authentication settings.
