[czottmann]

Go to Fastmail → Settings → Masked Email. There, click the "Edit" link next to the address you want to delete. On the following page, there's a big red "Delete" button. Works for me. :)

Update: looks like deletion only works when using the website, though.

[dannysu]

Ah thanks. Currently out so didn’t check the desktop website. Hope the delete button can work on mobile too.

This is a great feature. I’m glad this will bring it to more people.