Emails vanish on Samsung mobile

[#1]

I've only just acquired a Samsung Galaxy after having had a Blackberry for years.  Previously emails that came in to Outlook Express on my pc also remained on my Blackberry so I could access either.  Now if I read them on the pc they vanish on the Samsung.  How can I retain them on both?  When I set "Leave a copy of messages on server" I get 2 of each on Outlook and still lose them on the mobile.  Is it something I should be setting in Plusnet or on the Samsung? Grateful if you keep things simple, I'm a pensioner!

[#2]

Easiest solution would be to access your mail using IMAP rather than POP3. This means you'd be reading your messages from the server rather than downloading them to each individual device. You shouldn't be having problems with your current set-up as long as both devices, however it depends how you have them set-up. If you log into Webmail can you see all of your messages?

[#3]

Thanks Bob.  I use Mailwasher, so having the setting "Leave message on the server" on this and Thunderbird  (to which I transferred from the now defunct Outlook Express), has resolved the problem to my satisfaction.  I agree, (not having the knowledge but having read pages and pages of info!) that it would be better to use IMAP instead, but it meant wiping out all the POP3 accounts and starting again with IMAP.  I was both lazy and slightly nervous about "clearing the decks" before setting up the accounts again.