[Fixup]

I started to have this problem since last night. I applied the MS fix, but still cannot reply to a hotmail address.

Update: sending out a new message to the same address is fine, just cannot reply to.

Update: Once I deleted the long (not very long actually) quotes, the replied message went out fine. Not sure if this is a Pocket Outlook issue or hotmail issue, caused by the length of the message or some content in the quotes.