Missing send from account

I have accounts with Gmail and Outlook,
incoming emails are OK on both,
but when I click on NEW the Outlook account is not listed and I can only send using Gmail.
I have deleted and re-added the Outlook account without effect.
This started last week, previously it’s been OK,
any ideas?

Go to Menu > Accounts and click on the General tab for the Outlook account. Scroll down to Services and tick the AirSync option. Click on Save & Close.

Gary,

brilliant, thank you.

Only puzzle is why it suddenly started failing,
I haven’t changed anything recently, Outlook?