Actually, all the "Use This Mailbox As" options are grayed out. Maybe setting the mailbox behaviors in my Apple Mail Account overrides these choices? Anyway, I know I'm in the wrong place for mail problems. But, let me share what I know about my situation, and maybe you can turn me over to the right person/forum who I will gladly work with to see if we can figure it out, unless it's not just me and there's a bug/issue between Apple Mail, Yosemite, and Comcast......
Please see below, and thanks for you time and efforts.
My configuration info: Macbook pro, Mail 8.2, Yosemite 10.10.4, IMAP account, Comcast Server.
Two months ago I had a laptop and used Apple Mail with a POP account to access my mail on Comcast.
I recently got an iPhone, so needed to change my Apple Mail account from a POP to an IMAP so I could handle an email only once!
However, after setting everything up, I’ve had problems with mail. The two most obvious are:
- Not all emails that I send get into the Sent Folder on the Comcast server,
- Draft Folder grows. Unneeded copies of drafts get created, and stay in the Draft Folder. They don't go away until I delete them.
- An Outbox Folder is created sometimes. Sometimes the email is big, sometimes it's very small.
All these occur intermittently and sporadically.
Possible related, contributing factors:
The IMAP path preference under the “Advanced” tab in Mail is blank which is how it was set up when someone from Apple told me how to set it up. Seems to work with it blank.
- Port under the “Advanced” tab in Mail is set up as 993. It sometimes, somehow gets reset to 143 at times. Not sure why, what this means. It's now 143 in my illustration below.
- Comcast server and Apple Mail connection seems degraded at times. Can slow syncing cause all these problems?
The curious thing is that I have checked with my addressees, and the 'missing' messages arrive as they should in their Inboxes. So why they are not also on the server in the Sent Folder is the question/problem.
I am BCCing myself on everything I send (reply, forward, etc.) to make sure I get my BCC copy. I’m sorta I guessing that if I get my BCC, then that means that the actual SEND operation occurred, but the failure point is somewhere in how a copy of the SENT email gets into the SENT FOLDER on Comcast....
My Apple Mail account info showing ports, mailbox behaviors, etc. follow:


<Image Edited by Host to Remove Personal Information>