[jkbl]

It's a measure to prevent multi accounts. Some people really overuse free offering. Either your domain/IP is on a spam list or your email server may be misconfigured.

[NVQXE23I]

How is this a measure? I have my own domain, so why would I make several accounts for your service? I just need one.

And labeling a domain as disposable, when it's clearly isn't, sounds a bit strange to me.

[jkbl]

People did that a lot to get new free accounts from disposable email services (You can generate 100 images/mo for free). Around 15% of signups were disposable email multi accounts (40% of email signups).

I use email verification API for this. It states to make decisions based on public email blacklists and lists of disposable emails. Cleary it's not perfect

[isuleman]

Well you can also block domains from fakemail.net to prevent disposable emails.