This has been a topic of discussion for the past 7 years without any effort on Shipstation's end to add this feature. It comes highly requested (http://feedback.shipstation.com/forums/126593-idea-archive/suggestions/6736736-trackable-fedex-fims-...) as hundreds of people have responded to the previous discussion board. ShipStation initially responded they'd take a look but never got back to it.
ShipFims integration with ShipStation has been delayed long enough - your customer community is asking for this. Please consider adding this integration.
Hundreds of customers
Welcome to the Community, we are so happy to have you here with us.
I was able to dig in a little deeper into this for you to get some information and pass your feedback directly to our product team. The idea linked above was archived on July 16th, 2018 as this was not on our roadmap at that time.
I can tell you that FIMS Mailview was looked into and investigated in early 2020, but currently, this is still not on our roadmap. This is not to say that this topic will not be a part of future conversations, but it is not prioritized right now.
Thank you for your feedback.
-Erin: Your Friendly ShipStation Community Manager