Best multi-identity anonymity-focused email client
Hi, I'm looking for a mail client that is well suited for managing multiple identities and can easily handle routing everything over an anonymity network.
I would use Thunderbird, but I think when you take it online, it downloads from all your connected email accounts. I want to "go online" at will toward particular email addresses, in other words I do not want my upstream mail provider to be able to associate my accounts in any way, including access time, assuming there is a large enough other pool of people using the same client/anonymity network.
Are there any that are well made for this purpose? Otherwise I will use the mail frontend over Tor or something, but it would be nice to have a lightweight client-side application too so I can keep my emails downloaded and delete them from the server.
I should clarify that I already have multiple email accounts, so extra aliasing is not necessary. I'm looking for an email client application I can run on my desktop which separates the accounts well enough from the email provider.
The difference is that the alias provider or destination email provider can associate all your accounts with your identity. I do not want to give this ability to either the alias provider or the email provider. It is a different threat model. (Please correct if I am wrong)
I did not say how many different accounts I have, but you can assume my separation of accounts is sufficient for my needs.