[runlevel1]

> an iOS email client many years ago that required a Dropbox login for some reason.

IIRC, that was Mailbox. Dropbox bought them a month after launch and then, sadly, killed it off two years later.[^1]

[1]: https://www.theverge.com/2015/12/8/9873268/why-dropbox-mailb...

[Mister_Snuggles]

Yes, I believe that's the one. Thanks!

I couldn't remember it, but with a generic name like Mailbox that's not a surprise.