Storing messages using POP account

[Mosquito1]

Hi,
I use a POP email account (not IMAP) and would like to understand, in which way incoming messages are stored on the server respectively on my PC.
When I check my emails on my PC, the emails should be basically downloaded from the server to my PC.

In the Thunderbird account settings there is the possibility to choose either to leave the messages on the server or not.

When an email is sent to my email address, it is firstly stored on the server, right?
The email is still encrypted on the server, right?
When I check my emails on my PC, the email is downloaded from the server to my PC, where it is decrypted, right?
Is the email stored in decrypted way on my PC, i.e. when I remove or change my private key, will I still be able to read the content?

What happens further in the following cases:

Thunderbird setting "Leave messages on the server"
--> pEp setting "Store messages securely" --> The email is still on the server and it is encrypted, right?
--> pEp setting "Do not store messages securely" --> The original email on the server is completely overwritten with decrypted contents, right?

Thunderbird setting "Do not leave messages on the server"
--> pEp setting "Store messages securely" --> Does anything happen? There should be no message on the server any more.
--> pEp setting "Do not store messages securely" --> Does anything happen? There should be no message on the server any more.

I use Enigmail/pEp version 2.0.8 on Windows 10.

Thanks!

[Patrick Brunschwig]

I use a POP email account (not IMAP) and would like to understand, in which way incoming messages are stored on the server respectively on my PC.
When I check my emails on my PC, the emails should be basically downloaded from the server to my PC.

In the Thunderbird account settings there is the possibility to choose either to leave the messages on the server or not.

When an email is sent to my email address, it is firstly stored on the server, right?

Yes

The email is still encrypted on the server, right?

yes

When I check my emails on my PC, the email is downloaded from the server to my PC, where it is decrypted, right?
Is the email stored in decrypted way on my PC, i.e. when I remove or change my private key, will I still be able to read the content?

No. By default, mails remain encrypted, and are only decrypted if you view them. That's true for POP and IMAP. You may create a filter rule in Thunderbird to store mails decrypted, but that's a separate thing.

What happens further in the following cases:

Thunderbird setting "Leave messages on the server"
--> pEp setting "Store messages securely" --> The email is still on the server and it is encrypted, right?
--> pEp setting "Do not store messages securely" --> The original email on the server is completely overwritten with decrypted contents, right?

No. With POP nothing is ever written back to the server (except for deleting the message). Everything happens locally. The sent mail is either kept encrypted or decrypted, but locally.

Thunderbird setting "Do not leave messages on the server"
--> pEp setting "Store messages securely" --> Does anything happen? There should be no message on the server any more.
--> pEp setting "Do not store messages securely" --> Does anything happen? There should be no message on the server any more.

Same as above.