As per the recent visit to Apple forums, a number of iOS 9 users have been suffering from their inaccessibility to download attachment from their POP email accounts. This does not seem to be a bug; rather it seems to be intentional move from Apple, as the issue was not resolved in the latest iOS 9.0.2 as well.
Here’s a snapshot of the issue found from Apple public forum:
There isn’t any reply from Apple on this issue, except one given below:
“This issue usually starts if one of the devices/computers that was setup with this email account has been configured to remove a copy of emails on the server. If this is the case, the customer will need to check the settings of all the devices and computers that are running this email account.
iOS leaves messages on the POP3 server by default. iOS never stores email permanently, whether POP3 or IMAP. If they are removed from the server by another device then this issue can occur.
A test that you may want to do to confirm this is to have the customer produce the error by opening one affected mail on the iOS device, and then locate that specific email on his webmail. If not found, then the device is behaving as expected. If found, please try to forward it to the same mailbox and see if the same issue occurs.”
The resolution seems to be useless, even if you setup a POP email with an option to remove the copy of email from server, the email should stay on your iPhone or iPad. It is not possible to have internet connectivity all the time.
We have tried different tricks to resolve the issue like deleting and adding back POP account and resetting network settings, but these do not seem to work. However, the above response from Apple engineer gives a gloomy picture, that it is not a bug and rather an intentional move on how the Mail app works. As of now, the best possible fix is to use a third-party mail app, even though it is not a permanent solution.