https://www.emailnator.com/ generates @gmail accounts, harder to detect, but some services still might detect it

duck.com is great and I've only ever had a few times where it wasn't accepted.

Well this is awful. My policy is if it can't agree to my terms, it is rejected. If a company is kicking up a fuss because I want to ensure my primary address isn't forever compromised by spam, and doesn't work with aliases or duckduckgo privacy relays, then said company doesn't get my attention or business. Whatever the service you're trying to obtain from them, I can almost guarantee there's a more amicable alternative.

It isn't really about detection, they just got a blocklist of domains. There is not much temp mail services can do. Using lesser known or self-hosted solutions usually helps.

I actually just went through this because I previously used iCloud's Hide my Email service, but I'm de-Appling so I had to find something new. I've used Hide my Email, Firefox Relay, and Addy.io.

Hide my Email is hard to replace because it's shared with the entire @icloud.com address pool, so it's hard for companies to reject and it's hard to link all of your aliases together.

I ultimately settled on a combination of having a Tuta paid plan, which gives you a few email addresses, and Addy.io. I chose Addy because it's run out of Europe (the UK specifically) and has some great power user features while still offering easy-to-use apps for all of the platforms I use. I've only had Steam reject an Addy address so far.

At the time, I also thought Firefox Relay only allowed you to use your custom domain, but they do allow you to use the more generic @mozilla.com domain as well for better anonimity. Firefox Relay does have a limit to how long you can reply to emails you've received, though (I believe it's 90 days), it's run out of the US, and I think Mozilla has done some questionable things recently with respect to privacy.

I didn't check out SimpleLogin since it's owned by Proton, and I didn't check out DuckDuckGo's offering because I believe it's also a US company.

Something like https://relay.firefox.com/?

https://temp-mail.org/ has usually worked well for me, issues aren't too common, but they can be detected. Maybe make a throwaway Proton email and use their alias feature? Proton aliasing is good and bypasses temp mail detection from my experience.

I guess it depends on the specifics of what you are worried about. I have a catchall set up for a domain I own, and so I can make up an email on the spot. I've never had trouble getting those accepted.

But for random internet stuff I tend to use either Firefix Relay or Simple Login. I use these most of the time and don't normally have issues, but if I do then I use my own domain.

I think these relay email services (which are not temp/disposable emails btw) let you set up with your own domain too.