rye9 said:
So if I delete this, I dont have to do anything to get my settings back?
You will not lose any e-mail (the messages themselves) but you WILL lose preference settings if you delete the plist file. That's why this is not the first choice when there are other actions to try that might help. I haven't deleted a Mail preference file since last year so I don't remember which settings you retain and which you lose. It would be wise to save info about your preferences if they wouldn't be easy to re-enter. For example, note any complicated rules you have in the "Rules" section of your Mail preferences. And to be extra cautious you could back up the files in your home directory before touching anything.
Deleting preference (plist) files is a commonly-used technique when a program seems confused for no good reason. The tradeoff is usually the same - you "reinitialize" settings that can fix problems, but you have to re-enter preferences within the application. The Safari web browser even has a builtin way to do the equivalent: the Safari -> Reset Safari menu choice.
You
could choose to wait a bit, to see if another forum member posts here with (a) other sugestions and/or (b) the exact answer about which preferences you lose by deleting the plist file.
Carefully looking through all of the current preference settings should always be one of the steps to take before you "reset" a program. Since you said "my account settings are fine", we'll assume that's true. If not, be sure to check them carefully, including the "Account" section's three tabs (Account Information, Mailbox Behaviors, and Advanced) and the information behind the "Server Settings..." button on the Account Information tab.
Would resetting the preferences even possibly fix the problem that the outgoing mail server rejects my "address" as it calls is?
Since we don't know WHY that happens, it's POSSIBLE that this would fix it. If you can learn more, such as whether your mail account works with another mail client application, or whether other Macs can use Mail to send mail through the same mail server you are using, it would be help narrow down the problem and make it easier to guess whether the problem is in the preference file, is something set wrong in your current preferences, in Mail itself, on the server, etc.