In an email program, the outbox is a holding area – a place where messages go after you click Send and wait until the program can forward it to the mail server. The outbox helps you do other things in the email program, so you don’t have to wait for the mail server.
Let’s talk about the outbox. Many different email programs use an outbox and because you didn’t say which email program you’re using, I’ll use Outlook in my examples.
In Outlook, doing a Send/Receive (pressing the F9 key) causes the program to send anything that’s in the outbox immediately. If it doesn’t, Outlook should display an error message, which you’ll use to fix the problem.
Now, there are several different possible reasons why a message might get stuck in your outbox.
Your computer is not connected to the internet. If your email program can’t connect to your email server, it won’t be able to send the message.
The SMTP configuration in your email account might be wrong. That’s separate from your POP3 configuration. SMTP is the protocol the email program uses when you’re sending an email. You need to make sure that this configuration matches what it’s supposed to as defined by your email service or ISP.
Your email provider could be the one having problems. Check with your email provider to see if there’s something wrong.
It’s possible that your ISP is blocking or altering outgoing mail. You might experience this when you’re traveling. For various reasons, hotels sometimes either capture or block SMTP email traffic to prevent spammers from sending all of their spam from a hotel room.
It’s also possible that the email program itself is the problem. In that case, consider a repair install of that program (if that option is available). You may have to reinstall the program or reconfigure the email account from scratch.
Those are my recommendations. Start by clicking Send/Receive, see if you get an error, and note the specific messages that appear.