Sadly, one solution doesn't fit all issues that El Capitan has created.
I deleted my POP account and now I am unable to enter it anew.
I have had it confirmed by my ISP provider that the information I'm enetring is correct and they have refrred me back to Apple but it was Apple who asked me to check with my ISP provider, when they were unable to correct the problem online.
All I want to do is to get my email to my iMac from the mail webserver but what used to work doesn't since the installation of El Capitan.
If there were a simple solution to the myriad of issues created not just to mail but to a whole host of services since El Capitan, then Apple would have either released a statement informing people how to correct the issue, or they would have released a patch via an upgrade to correct the issues that have been caused by the new OS.
They have, so far, done neither.
Forum contributors are to be applauded for their constant attempts to have these issues resolved and sharing these with others in the hope of of correcting those issues and some have been blessed with resolving those issues but others, like me, are still left in limbo.
To issue a statement of how to correct the issue would place them in the position of admitting that they have created a problem in the first place and their arrogance prevents them from doing this.
I am a big Apple devotee and am disaapointed by their default defence, when anything goes wrong they buy time by passing the blame to others, when they know the issue is of their making.
When Apple get things right it is impressive but this also applies when they get things wrong, they too are on an impressive scale as the El Capitan forums confirm.
I, simply, want to be able to have my mail delivered to my iMac as it used to be pre-El Capitan.
I live in hope that one day this will happen.