Help email stuck in outbox

[LilArgie]

I have my Verizon email set on my Evo. POP account - incoming.verizon.net server port 110 - outgoing.verizon.net server port 587. Everything works fine however sometimes sending videos via email and a few emails will get caught in outbox and never send. I get notification that it could not be sent because account settings are wrong. Yet others I may send after go thru fine. Can't delete them from outbox because when I try to open I get a message that I cannot open a message while sending. Only way to clear it is to completely delete account and then add again. That doesn't make sense. Any idea why this is happening?