Internationalized Email Addresses, for example প্রোটন@তৌহিদুর.বাংলা is not supported by Proton Mail. When I type my email address in Proton Mail, it weirdly tells me address is not valid.
Note that popular email service providers such as Gmail supports this.
To Reproduce:
Try to send an email to the email address given above.
I’m not surprised. Internationalized symbols can be used to make an illegitimate email address look like it’s from an official one.