Emails delete within 5mins from handset if not saved to server

[AC Question]

Hi
I have a new Samsung Galaxy S5.
I currently don't have emails being saved to my server with my LAptop as I find my mail box fills to quickly.
However If I don't click "save to the server" my Samsung mobile deletes the emails from my phone within 5 minutes.
I do not save them to the server as when the mailbox gets full and I have to delete the emails off the server it also deletes them off my phone and I cannot afford that as it is a work phone.
The other issue I have is if I don't save it to the server, and my laptop is on, the email only goes to the laptop and not the handset.
Any feedback would be welcomed.
Samsung and Optus do not know why this is happening by the way and I have spoken to multiple technicians within their businesses.

 

[CTW_949]

Assuming the account settings are correct to ‘delete from server’, I found that ONLY by SWIPING the email(s) into Deleted Status followed by a ‘Refresh’ would actually delete emails from my server.
...good luck