This app was mentioned in 2 comments, with an average of 1.00 upvote
I'm assuming this is an Exchange engironment? I've personally set up Touchdown for Exchange with SMIME, but that was at an older job. I'm currently using Nine for Exchange, which apparently supports SMIME, but I have not set it up yet. It looks like Samsung's native email app supports SMIME for Exchange, but not the native "pure" app.
Also, keep in mind that with a certificate, you have two pieces: a public key (which is generally the certificate), and a private key. You need both. In some environments, you may even have two key-pairs; one for receiving encrypted emails and one for signing outgoing emails. But a private key should never really be downloaded from a website. Generally speaking, it is generated on the client device (which is probably Outlook if you are using Exchange and your VIP using Outlook as your desktop client with SMIME). So I am not sure exactly what you are downloading, but it may only be one piece of the puzzle.
EDIT: I should point out that both of my examples above are paid-for Apps, but they both allow for a 30-day trial period so you can make sure it works before committing to buying it.