Now I'm confused!
I thought you wanted to use POP with your gmail accounts, but you seem to have them all configured for IMAP 🤔
See the difference between POP and IMAP:
en.wikipedia.org
en.wikipedia.org
You cannot mix the two.
An account is either POP or IMAP.
I'm puzzled as to why you need to edit the SMTP server list.
If you simply create a new POP account giving it a description (I use the name before the @gmail.com),
as I explained above, you will see that the name in the server list is configured automatically. You shouldn't need to have to do anything else.
Apart from my 3 gmail accounts, which all share the same POP and SMTP servers, I also have have several other mail accounts on various hosts, including my own domain, and they are all visible in the server list.
The only IMAP account I have is iCloud, and it's true that although it is visible in the SMTP server list popup, it is not editable.
I'm following this thread as the past 2 weeks have been a nightmare - following Google's 30th May threat to eff up Apple users using Gmail in Apple Mail.
The work round I found was as follows:
I'm using a Macbook with OSX 10.13.6 and using multiple Gmail accounts in POP.
Went into 'Manage your Google Account' on the right side drop down menu in Gmail in Chrome
Once in that look at menu on left and click: Security
Scroll down and click the: 2-step verification
Click the 2 step verification
Click Get Started
Sign into your account
Put your mobile phone number in & choose text or phone call
Click Next
Enter the verification code you get into the red section
Click Next and then click Turn On
NEXT
Go to the app store on your phone and get the Google Authenticator App
Open the app and scan the QR code
Click next and add the code into the box on the Change authenticator app
Click Verify
Then go back to your gmail account security page
Scroll down to App Passwords
Click the > next to this and sign into your account again:
On the next screen:
Select the APP - Mail
Select the device - MAC
Click GENERATE
and you get a code
Go back to Apple Mail
Go into preferences
Then go into Accounts
Replace your normal password with this Google app password
Sort out the various Google Gmail security emails and its done.
BUT - on some accounts I had to get this code a number of times before it worked.
And THEN today a week on from faultless service - suddenly all my SMTP settings except one said NONE. As with the previous person - every time I try to add a new SMTP server for one of my email addresses it 'kidnaps' the one that works from my 1st email address and sends from that email address rather than the one I want it to send from. Next time I try to send from that 2nd email address its gone back to NONE on the SMTP setting and won't work at all and only the 1st email address sends.
I've tried it with many different gmail addresses and the same happens every time.
Nothing at all works.
To my mind its now a case of dump all use of everything to do with Google or dump all use of everything to do with Apple. If Google is going all out to stuff Apple I'd rather go back to Apple everything than put up with this utter rubbish situation.
A really good workable way of multiple multi-national tech companies working their stuff together's gone up the shute because of tech greed. Maybe some will see it another way. Maybe - I HOPE - someone will find a work around that works for more than a week?
Any ideas welcome or I start to search for a new email address server that isn't a pain like Gmail has just become.
It all seems to work now. 
