Why cant I send an email with my cell phone?

I can receive emails and before I could reply, but know I get emails and reply but the reply emails never go out. There is no message that I know about indicating the email didn't send. I learn later (too late) when I check the sent messages from my laptop/

Which email app are you using? Gmail periodically has outgoing emails stuck in the outbox. Go into settings-apps and clear the cache, that usually helps.