Outgoing Mail Server List (El Capitan)

I have a similar problem after upgrading from Mavericks to El Capitan. My "outgoing mail server (SMTP)" list shows a number of blank/empty rows, 3 real SMTP servers (some obsolete), but there is no option to edit or delete the SMTP servers. I have tried deleting and re-adding my e-mail accounts, and have also tried deleting the Mail application data and preferences in the Library folder and re-adding my accounts from scratch. I also tried switching the "Automatically detect and maintain account settings" option on/off multiple times. But nothing has fixed the problem so far. And when I select one of the SMTP servers from the list, when I come back to the mail preferences the SMTP server has been reset to "None". I am VERY frustrated at this point!!! Any new ideas from other with similar problems (other than switch to another e-mail client or switch to Windows) would be appreciated.

Okay, I think I was finally able to fix the problem. I haven't seen any other solutions to this specific problem, so I'll post what I did to try and help others:

1. Backup and/or export your existing mailboxes before you begin...
2. In the Mail application preferences, I deleted all my non-iCloud mail accounts (in my case I deleted my POP accounts from my cable ISP, but I kept my iCloud account).
3. Quit the Mail application.
4. In System Preferences, go to Internet Accounts, select your iCloud account, and then turn off (uncheck) the Mail option.
5. I also removed the POP and SMTP passwords for my ISP e-mail accounts from the login and iCloud keychains using the Keychain Access utility (I don't know if this is necessary or not).
6. Open the Mail application, create an e-mail, and then try to send it. Hopefully, you will prompted to select an SMTP server (since the iCloud account is "offline"). There should also be an option to edit the SMTP server list. I removed all the SMTP server entries (except the entry for my iCloud account I think, but I may have removed them all).
7. Quit the Mail application.
8. In System Preferences, go to Internet Accounts, select your iCloud account, and then turn on (check) the Mail option.
9. Open, the Mail application, and go to Preferences, select the Accounts panel, and check the "Outgoing Mail Server (SMTP)" list. In my case, the blank/empty entries had disappeared and the option to edit the SMTP server list re-appeared (YAY!!).
10. Re-add the e-mail accounts you deleted in step 2, then import any mailboxes that you backed up if necessary.

It's possible that you don't have to delete your e-mail accounts or delete the keychain entries for this to work, but I had already done that in an earlier attempt to get things working again. I usually wait for the first bug fix version to be released before upgrading (and I skipped Yosemite), but I decided to go ahead and update to El Cap without waiting. I'm VERY frustrated that I had to waste so much time fixing something that should be rock-solid in any modern operating system. In every other respect though, El Cap seems to be working well so far (fingers crossed)...

Thanks so very much for this answer Novakevin01 which worked for me after all the failed attempts. All references were to the Edit smtp list but it wasn't there as an option. I basically followed your approach ensuring I only had iCloud account as an option and then proceeded as you suggested. Having started my career in 1969 teaching university graduates to program computers in the days of punched cards and line printers, and having had to debug a program suite for a local government organisation whose programmer didn't flowchart his ideas, I know the need for clear testing of new systems. I find it incredible all these years on that computer companies still haven't come up with a way of automatically checking their software before launch for some of the most simple issues, e.g. is someone's email still going to work after El Capitan is installed.