Hello Domme Lynx

I have never used Protonmail but I feel your pain in dealing with unreliable email. I started having issues with the major ones (Gmail and Yahoo and Outlook - yes I have had them all over the years) so I searched for a private provider and was willing to pay for it. Email is important and worth a few bucks a month to make sure it works. I've been using a company called Luxsci for about 3 years - well before the FOSTA/SESTA mess.

https://luxsci.com/

It took a little getting used to and it's not perfect but it is reliable and they have amazing customer support - most issues are dealt with within minutes.

Anyway, hope this helps.