I'm having a hard time finding how to access about:profiles, but in looking for this I found you can disable the "download messages on startup" option. Maybe Thunderbird is the solution. It will require some more investigation, but this is giving me hope.
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.
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.
To be honest, I didn't verify the signature when I installed it. The download is over TLS (HTTPS) so you know you have a secure connection with the F-Droid server during the download. But because of the tiny chance the F-Droid website was hacked at the time you download it, you should verify the signature.
I'm having a hard time finding how to access about:profiles, but in looking for this I found you can disable the "download messages on startup" option. Maybe Thunderbird is the solution. It will require some more investigation, but this is giving me hope.