[Abishek_Muthian]

I stand corrected[1], premium users can 'Combine multiple accounts into 1 account'.

[1]:https://protonmail.com/support/knowledge-base/combine-accoun...

[wanderfowl]

Yep, that's fine, but it's not much of a firewall. And unless I'm mis-reading this, this doesn't allow you to combine multiple domains.

[lfms_dotfile]

I've setup multiple domains on the same Protonmail account. You can create new addresses (@protonmail.ch/protonmail.com/pm.me/domain) with a paid account (iirc up to 5 total addresses with Protonmail Plus).