I have completed the previous missions as stated by the wiki but this mission is not showing up on my mission list. I have definantly done the previous because i have the 4 kronyn anomaly engine things. Is there any other pre-requisits??

Im rank 250

even though you may have done the entire Returning the Message mission when it was a timed mission, the entire Kronyn chain has to be completed...
if you had skipped or only partially completed ANY of the following, the earliest of these missions that hadn't been finished will appear in your mission list

Anomalous Appearance
Aberrant Signals
Future's Admonition
The Aevax Experiment
The Kronyn Exodus
Returning the Message
Altered Directions

If any of those missions show up, even if they've been completed, click them. For one of the mission chains I completed the first mission, skipped one, then completed all the ones after it. The second mission later showed up, and when I completed it, the next mission showed up - even though I had already completed it - but it just had the complete mission button. On clicking it, it cycled to the next mission, but since that one had also been completed, the same thing happened again. After a couple of clicks though, the chain disappeared and was all sorted. So just click whatever missions are showing up, complete them, and the game will work out the issue.

Yep, haven't done the anomulous apperance yet. Do I need to fully complete it or is one completion enough?

Full. Better start collecting flux probes...

If you need Flux Probes, post in the Trading Post forum section. Someone might be able to sell you the probes you need.