Downside is you have to use 1password AND fastmail obv.
Random addresses are also somewhat problematic too when they ask me to “confirm my email”. But they just think I have a very strange username.
I just use a random cheap domain, registered through Gandi. This includes a couple of 3 GB mailboxes each with unlimited aliases, which is quite adequate if you don't use your email as a file store (much).
I suppose the "right" way would be through something like Fastmail instead, but the simple arrangement above has worked fine thus far.
They use something called Jellyfish for spam detection and it's been pretty impressive. A few false negatives but overall catches most of it. And you can use their webmail or any IMAP/POP3/SMTP client.
A bit slow but I don't think it's unreliable. If it is, that's scary because how would I know :)
Just moved a folder with 1037 emails and it has 1037 on NameCheap now. Seems like it moved them all! (And it didn't take too long. It's moving a bunch of subfolders now.)