Mac Mail acting up, can't fix

I'm having problems with Mac Mail which I cannot seem to fix. I've tried several "fixes" I've read online (see below) but none have solved the problem.

My system: 15" MBP retina OS 10.8.2

Basic problem: Mac mail has been my mail client for several years. Last month it suddenly would not let me send emails from my home WiFi, but I could receive emails fine. Sending messages yielded "Cannot send message with server... content to the server failed" Listed outgoing servers were correct, but labeled as "offline". However, mail still worked fine at work for a while; no problems. Now I have intermittent problems sending mail with etiher of my two different email accounts via mac mail. Still receive emails fine.

Fixes I have tried: I changed ports and toggled SSL on/off, using ports 993, 25, 51, 465 and 587 as suggested. I deleted all my accounts completely, then went into Keychain access and deleted all stored passwords and secured trash, then reinstalled my two email accounts. Emails reloaded but the same problem remains. Weird thing - when I deleted my accounts and reinstalled my two current email accounts I also deleted three "inactive" email accounts from previous jobs. I did not reinstall those. However, now when I try to send an email they pop up under "Edit SMTP Server List" even though they are no longer installed on mac mail. I also get the choice to use that outgoing mail server in mac mail (even though I deleted it... or thought that I did. They do not show up when I go into "accounts)

Sending emails from work is intermittent. This mroning it worked fine. This afternoon I can't send at all.

Also, my girlfriend can send and recieve emails fine on her MPB from our same WiFi. Checked her settings against mine and they're identical.

I also followed the steps outlined in Apple's help page.
What's confusing me is how the problem is intermittent. Because I can sometimes send emails I know my SMTP info must be right.

can anyone help me fix this?

No, they aren't - one's a MS outlook, the other an AOL address. also have a gmail account that had the same problems (wouldn't allow me to send emails from certain locations), but I deleted that one when I tried to reinstall everything.

No antivirus software other than apple updates, no firewalls besides my basic WiFi password, but that's the same for all the other computers accessing. It seems the problem is specific to something with *this* computer. not aware of any malware but that of course suggests that i should scan my system just to be sure. let you know if i find anything. for now my issue STILL IS NOT SOLVED (i'm getting frustrated, as you may be able to tell)