PopMan

There is no option for marking mails an unseen on server. What woul be the use case for this? Usually, you only load unseen mails from the server anyway.

There will be no OAuth 2.0 support in PopMan.

PopMan does not support OAuth 2.0.

So if App passwords won't work anymore, then you can not use PopMan for it.

You can create an App Password and use that as the password in PopMan (ignore the "Sign in with Google" button):

https://support.google.com/mail/answer/185833

You can find the settings in PopMan Account dialog by clicking on the small button with the "..." right to the protocol drop down.

As far as I understand, Yahoo will require special "App password" at some point: https://help.yahoo.com/kb/SLN15241.html

Make sure the IMAP settings in PopMan look like this:

Mailbox = "INBOX";
UseSearchCmd = "true";
Criteria = "UNSEEN UNDELETED";
IgnoreMailboxNotExisting = "false";
TLS = "true";
Expunge = "true";
FastMode = "true"

It is not possible to use OAuth2 in PopMan.

For Google Mail and Yahoo Mail, there is the option to create an "App Password".

https://help.yahoo.com/kb/SLN15241.html

Follow the instructions to create an App password: https://support.google.com/mail/answer/185833

Then use this App password for the Password in PopMan account (Ignore the "Sign in with Google" button).

=> Dropping OAuth2 support and expecting App Password for the PopMan account

Instead of using OAuth2 and the "Sign in with Google" button in PopMan, you can create an App Password and use that as the password in PopMan:

https://support.google.com/mail/answer/185833 

Instead of using OAuth2 and the "Sign in with Google" button in PopMan, you can create an App Password and use that as the password in PopMan:

https://support.google.com/mail/answer/185833 

What protocol do you use in PopMan?

Just to be clear: You already can block entire domains.

However, you can not add a domain to the blacklist using the context menu.

Welchen Installer haben Sie denn verwendet? Den regulären von der PopMan-Webseite? Oder das ZIP-Archiv? Oder die Portable-Variante?

I don't think this makes sense: PopMan does not remember emails beyond sessions. This might people believe that there were no emails in the last check.