Hello,
I would like to join the conversation, and help.
I agree with what Palmetto_CharlieSpencer said, a 100% migration to the cloud isn't necessary a long term solution.
My experience in a web archiving company taught me that In-House customers are more satisfied than cloud ones. I believe for non critical mission cloud can be a good alternative, but i do not agree on costs.
for these reasons: 1-hardware is getting cheaper and cheaper.
2-some costs and annual fees for the cloud are not justified, there is a lack of transparency in the pricing system (I remember working for a cloud service provider, who was charging setup fees (incredible amounts compared to the work of installing remotely a software or for a first crawl))
3-There is turnkey solutions (hardware+software) of course not suitable for email archiving, i am talking about bigger investment. You will only pay for the support which is supposed to be less than 8% of the purchase.
As an IT marketer i encourage In-house investment when you have to buy a big solution for the long term.
hope i helped!
regards