You do not provide enough information for anyone to be of help. Which account are you experiencing the problem with? POP and IMAP accounts function very differently:

- POP accounts pull all email from the server to whichever device you log into the account from.

- IMAP accounts keep the emails on the server until you delete them from your device, allowing you to sync email across multiple devices.

Which if your accounts are you using? Which if your accounts are you experiencing issues with?

If you are wanting to sync email across multiple devices, a POP account will NOT be feasible. Use IMAP or an Exchange account.