Emails are coming in, but not going out

I have just realised that my emails are not being sent from em client, it works fine in gmail directly, but for some reason they are stuck in my outbox, when sending from em client. I do receive emails in my inbox, though. Thanks for your help!

As a test, can you completely disable any anti-virus, firewall, proxy or VPN, then try send again.
Sometimes even restarting your router may resolve this.

Hi Gary,
That seems to have done the trick, thanks so much for your quick reply!