Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
This is a known issue with Apple Mail in Ei Capitan. We have to fix one by one. First lets fix iCloud. Quit Mail. Then go to System Preferences > iCloud. Uncheck Mail in there. Wait 1 minute. Then enable it back.
Open Mail. Click on Mail menu and select Preferences. Under Account, select iCloud. From the "Outgoing Mail Server (SMTP)" pop-up menu, choose Edit SMTP Server list. Under Account Information, change the server to smtp.mail.me.com (even if is already there, remove it and enter it again)
Close it and restart Mail. Let me know how it goes, so we can move to next step.
Can you delete the email account and add it back ?
First turn off Mail from System Preferences > iCloud. Then delete the email account and add it back. Do the same for Comcast and MSN. This will re-establish the connection with server.
Remember this will delete the emails from Mail. But as long the emails are on the server, they will be downloaded back. So make sure the emails on server by checking from Safari.
Do a backup before deleting the email accounts. To do that, select one or more mailboxes, then choose Mailbox > Export Mailbox. This will backup the mailbox.
I'm glad you got comcast working again. As long as they are on iCloud, they will be synced back. This is an known issue that affected many users - not your fault but Apple's. They probably fix it in the next update which is very likely to be come out soon. Try this. Turn off Mail from System Preferences > iCloud. Don't turn it on yet. Goto Mail > Preferences. Click iCloud and are you able to edit SMPT server list now ? If not, close Mail. Enable Mail back in iCloud. Check Mail again.
Also click on Mailbox menu and select Take All Accounts online. If it still not working, then you will have to delete iCloud and add it back.
Excellent ! Keep me updated please.
Hi there, I'm just checking. How is it going ?