A server error needs to be fixed by the owner of the server. That's the company that handles your email.
But in this specific case it probably means that you want to send your mail from an another account than you're logged in to. Anyway, the customer service of your mail provider (the one you're logged in to when sending this message) can tell you why it happens and how to prevent it.
It's not an error in your software, it's simply that you use it in a way not supported by the mail provider. So the fix is: do it the right way.
When I send an email on my Outlook 2010 the email is returned stating: "Server Error 554; Relay Access Denied.
I am using Windows 7 [64 Bit] on a DELL Model N5110.
Could someone please tell me how I might fix this or of a reputable download repair where I could pay to have it repaired?