Hi @pendantry, I'll pass your confusion back to the designer, but to answer your questions:

1. It is recommended to use the @mozmail.com domains when you can, because they cannot be linked together. The advantage of the subdomain is that its aliases do not need to be generated in advance, which is useful e.g. in physical situations. Any email sent to [email protected] will be forwarded to your email address.
2. Yes, your reply to [email protected] should go to the original recipient. If you were to send a direct email to the recipient, Relay would not be involved and your sender email address would be visible to the recipient.

Hi @Vinnl , thank you for your very prompt and helpful response.

However, you've used the word 'should' in "Yes, your reply to [email protected] should go to the original recipient.". I've seen that word used before. Thank you for confirming that it 'should' do this: the question is: does it? It would be far better if the system could confirm, in some way, what address the email reply is actually being sent to. If it is not possible to do this in the 'To:' field of the reply email (and I can imagine that perhaps this is the case, there being a multitude of email clients, all with their own behaviours, and it might well be impossible to accommodate them all), perhaps Firefox Relay could send an autoresponse confirming that the email reply had actually been forwarded, and confirming the address to which it had been sent. (I admit that the latter would not be ideal, as we're all already drowning in email as it is...).

Yep agreed, I brought up that exact suggestion with the team :)