MicrosoftLog a support ticket with microsoft.
They will give you the fix.
However the next issue is that O365 as threshold limits on 30 emails per minute and so many per hour , per day etc.
So if you sending 100 emails in a go it will bomb out. There isn't any pretty solution to overcome that yet. Been playing with a throttling pipeline but that causes biztalk to slow down and run out of threats. Another idea is to write email jobs to a table and then fetch them from there with polling and the fetching bit of code to obey Office 365's threshold limits... etc...
I haven't solve it yet for me, and we regularily sent more then 30 emails per minute...
