Problem Sending Messages Using the Messages App

Hi everyone. I'm also asking this elsewhere in case I don't receive a response here. It has recently come to my attention that I cannot send messages using the Messages app on my mid-2013 MacBook Air. I can only receive them. I know this because just this week I asked my neighbor across the hall to try and send me something. He did, and I was notified of it yesterday when I returned from a work-related outing. I asked a friend and coworker if I could try sending him a message, and I did that just this morning. The only way I can send text and voice messages is if I send them to myself, which is rather pointless. Anybody else experiencing this issue? I have the latest build of OS Sierra.

Forum: 

a couple of troubleshooting questions

firstly, is this a text message you're trying to send, or iMessage?
If iMessage, did you try signing out of your apple ID, and signing back in? If not, that is what I suggest you try first.

Seems to Work Now

Hi and sorry for the delay in responding. My wifi has been acting up during the past week or so, but I think it might have resolved itself. But anyway, I'm sending these using the built-in Messages app on my computer. I didn't think there was a difference between that and texting, but perhaps I'm missing something? Anyway, the problem seems to be fixed at least for now. I'm going to try deleting some unneeded stuff on here and see if that helps any. In addition, I added an extra letter to my friend and colleague's email address. I think his actual last name is one letter too long for the email address he is using. At least this is what I heard a long time ago: that the first part of email addresses can only be like 8-9 characters or something. But when I tried sending him a message again I got the sound to indicate it was sent successfully. When I have more time I'm going to see if he has replied yet, but I think so because my cell phone keeps notifying me of new text messages. As you can probably guess I'm still rather new at this whole texting thing.