I appear to have found a fix, though it was a bit of a fluke.
I run multiple inboxes, and my issue was that 3 out of the 4 outgoing servers was showing as "offline", therefore any email I sent, no matter which email address I intended it to go from, they all sent out of the one, which was a business account - not what I was going for.
I discovered that somewhere along the line some passwords had gone missing. The fix (at least how I fixed it, if there's a less roundabout way of doing this, please let me know).
I don't know if these directions will work unless you're running multiple email accounts, but this is how it looked for me.
1) Compose a fresh email.
2) There will be two drop down menus below the address fields. One is the "from" email address, one is for the outgoing server. Select the outgoing server drop down menu
3) Select "Edit SMTP Server List..."
4) When the list appears, select each active server from the top and make sure there is a password entered. In my case, the 3 out of the 4 that weren't working had the password field blank (also make sure none of them have "use only this server" checked).
Once I filled in these passwords, it all seemingly began working again.
If anyone has a quicker way of getting to the "Edit SMPT Server List..." page that would probably help.
Hope this helps someone out there.