The POP3 mail protocol was designed, and is implemented in many cases, to support one connection at a time. If your email provider is not configured to allow multiple connections, then when two different devices attempt to access the mailbox at the same time, both devices may get locked out or you may be prompted to re-enter the password.
Try to have only one device access the POP3 server at a time. You can do this by:
- Quitting your computer's mail application
- Turning off devices you are not currently using
- Adjusting how often your device fetches email
Note: This setting is available on the device by choosing Settings > Mail, Contacts and Calendars > Fetch New Data.
If the POP3 mail account is locked out, quit the mail applications on all other devices and return to the Home screen on your iOS device. Once all email accounts are no longer accessing the POP3 account, wait for the server to reset the connection. This can take five minutes or longer before you will be able to retry. To make sure your device is not keeping the connection open, try turning it off.
If your email provider limits how often you may access your email account, set the device to check manually or configure Fetch New Data to check less frequently. If your email provider offers the IMAP protocol as a service for that email account, try setting up all devices to use IMAP.
If you are not receiving email messages you expect on a POP3 server, and you have received those message on another mail client, please see this article.