is the account IMAP or pop? Do you have other devices accessing the account, phone. laptop, partners phone, Ipad etc.? What mail provider?

Please tell me the consequences of POP or IMAP. Does one or the other cause the problem? Same question on other devices. Does another computer running Vista and Windows mail, configured to leave emails on the server, cause the problem? Is mail provider Peoplepc.com the problem? Is my third party email Thunderbird the problem?

Can you please tell me the consequences of POP or IMAP. Does one or the other cause the problem? Same question on other devices. Does another computer running Vista and Windows mail, configured to leave emails on the server, cause the problem? Is mail provider Peoplepc.com the problem? Is my third party email Thunderbird the problem?

It is presumably using POP in Thunderbird because that setting is not offered in an account that uses IMAP.

POP: mail arrives at the server. The client collects it, downloads to the user's machine and deletes the copy on the server, freeing up space for further incoming email. Your messages are stored on whatever computer they are downloaded to. Some email clients allow for copies to be left on the server, but it's a clumsy way to work an email account. Without knowing the whole story, we can't say for sure why Thunderbird isn't seeing copies being left on the server. As Matt was trying to find out, other devices might be downloading or deleting messages.

IMAP: all mail is stored on the server. Multiple devices (computers, laptops, tablets, smartphones) can be used to work with email. Since all refer to the same collection of messages and folders on the server, you see the same messages regardless of which device you use.

Question: why do you want to leave copies on the server?

This site:

https://psc.peoplepc.com/email/email-server-settings.php

…talks only about POP. So the IMAP option is probably not open to you, and TBH, is not going to be nice to use over dial-up.

It is possible that peoplepc configure their servers not to honour the commands used to leave copies on the server. The relevant RFC has this to say:

* Enforce a site policy regarding mail retention on the server.

Sites are free to establish local policy regarding the storage and retention of messages on the server, both read and unread. For example, a site might delete unread messages from the server after 60 days and delete read messages after 7 days. Such message deletions are outside the scope of the POP3 protocol and are not considered a protocol violation.

http://tools.ietf.org/html/rfc1939

Thank you very much for the reply and interest in my problem. My wife and I are running two notebooks; hers running Vista and Window mail and mine running Win7 and Thunderbird. Both are set to leave emails on the server. The reason is that if I download mail first, it is taken off the server and my wife never receives the mail. If she downloads mail first, I can then download and mail is deleted from the server. This causes too much synchronization. To work around the problem, I look at the mail on the server until she advises me that she just downloaded email. Thanks for whatever help you can offer.

It's because you are using POP protocol if both of you change it to IMAP it will be fix https://support.mozilla.org/en-US/kb/imap-synchronization

But it would appear that the mail provider doesn't offer IMAP.

I would suggest that you set up a second account exclusively for your wife. At the server, ie via webmail, set the first account to copy everything it receives to the new second account. Then what you do won't affect what she sees. Her new account could be set up for free with Gmail, gmx or similar. These providers let you register your other email addresses to use as aliases, so you can continue using your current address.

I've never known Thunderbird to disobey a setting to leave mail on the server. Maybe she already has her own account but it is treated as being secondary to your own?

As an experiment, what happens if you use Windows Mail yourself?