Hi there
Just so I'm clear, is she deleting the unwanted old emails from MailWasher once they are in Mail for Win 10 ? Will refer to that program as MAIL for ease.
There are two ways to access your emails from an email client, being POP and IMAP. What you are describing seems to be a result of the account in MAIL being setup as IMAP.
With IMAP, programs like MAIL leave the messages on the server and interact with the server directly. Meaning, delete a message in MAIL, it then deletes from the server. Move a message from the Inbox folder to another folder, the message on the server moves to this folder also.
This way multiple clients can look at the email account and see all the same messages.
Previously it would have been using POP to access the account, which works a bit different in that the emails it retrieves are stored as copies on the computer, and it doesn't keep itself synchronised the same way.
There is a few options though, ultimately depends how she wants to use email.
Option 1 : Keep using IMAP in the MAIL and also in MailWasher.
In MailWasher under Settings >> Accounts >> Incoming >> you can set the account to IMAP at the top >> Save.
Then under the Advanced options, there are some options to Download Read Email, leaving this unchecked means MailWasher will only retrieve emails flagged as Unread, if you Read an email in the mail program, this flags it as Unread and will remove itself from view. You can also then set MailWasher to only retrieve emails from the last xx days.
Keep in mind, using IMAP will retain the behaviour you mention, deleting an email from one program will remove it from view in the other.
But knowing that MailWasher will only load Unread emails in the Inbox folder from the last xx days, gives you some manageability over what emails show.
Option 2 : Use POP to access the account in the email program.
What probably happened in the past, was Live Mail retrieved the emails using POP, then deleted the copy off the server once it downloaded. This would have meant after she downloaded the emails into Live Mail, the next time MailWasher checked it would see the messages gone and remove them from view. Unfortunately MAIL is a very basic program and has no nice options for this.
If she wanted to use POP to access the messages, then I would recommend switching to ThunderBird
https://www.thunderbird.net/en-US/
It's not that dissimilar to Windows Live Mail, has many more options and it's free.
By setting that up manually with the account to use POP, you can then tell it to delete emails off the server once they are downloaded, so they disappear from MailWasher, and once an email is downloaded it exists just in ThunderBird.
If you go with the second option, let me know, there's a few other options to be tweaked.
Any questions, just lemme know
Cheers