I am having a really frustrating time atm..

(both laptop and desktop are using the same version of outlook with identical accounts)

Using outlook i am able to send emails from my desktop pc with no trouble.

Yet there are certain emails (only a couple) that i cant send to from my laptop.

I can receive emails from these people and have verified these emails are active and working from my laptop, using a verification program yet i get error 550 everytime i try and send something or reply to these addresses.

I am at a complete loss as to what is going on...