Ask HN: How to handle services that don't accept valid email addresses?

I recently migrated my email to a .network TLD and am having trouble with about 10% of the sites on which I try to use it.

Most recently was AAMI, an insurance provider. Their form tells me to 'Please enter a valid email address', which of course I've done. It's their aggressive form validation which is causing the problem.

I DM'd them on Twitter, followed up by email (from my perfectly valid email address), and they've told me that "due to the way our system is currently set-up, our online system won't be able to accept the email addresses you wanted to register with".

They suggested that I "use an alternate email address to register for these services", and I've advised them that, instead, I'll be taking my business elsewhere. But I'd rather not have to! I used them in the past, I like everything about them other than this.

Does anyone have any successful strategies for dealing with this sort of thing? It's not like the new TLDs are even that new any more. ¯\_(ツ)_/¯