Email migration is genuinely painful and I am sure there's a real market here, so I am not trying to discourage you. But why should I trust a third party with my IMAP credentials?
"Credentials encrypted in memory only and deleted immediately after migration".
I have no way to audit/verify this claim. You're essentially asking users to hand over the keys to their entire email history on faith.
Yep, and no ISO 27001 or SOC II, nor is the location of the country of operation disclosed, let alone any name associated with it.
I remember about 20 years ago writing a relatively simple tool in perl with IMAP::Client to migrate a Universities staff mail from Courier (I think) to Communigate Pro, and then another one to migrate from Communigate Pro to Microsoft Exchange a few years later.
I was at the beginning of my career. It was pretty easy. Went almost flawlessly, moving thousands of peoples email.
Where is the "painful" part? It's just moving blobs of text around.