Default [Q] Emails hanging in outbox

Moto X - T-Mobile

Added a new Exchange email account on the phone last week and all of a sudden I'm finding that emails are getting hung up in the outbox (using stock email app). Seems worse when on WiFi which could be an ISP issue, but also happening when on 4G LTE.

Happening on multiple accounts so not just limited to new account.

Any ideas?