I'd have to agree with AE4RV, give Comcast Support a call.
I'm not quite certain where zimbra falls into play here (unless you're just referencing that's the webmail software Comcast uses).
When I'm at the Comcast site (which I think you call WEBMAIL) reading my XYL's email, this is the first part of that site's address:
........"; notice the word 'zimbra'.
Had I not, earlier in the day, read about 'zimbra', I would not have even noticed 'zimbra' there.
BTW, had I pasted the entire address, anyone could actually see her emails.
When logging into Comcast, you should see: Inbox, Sent, Drafts, Spam and Trash. If you see other folders, you may need to have your email account reset.
When logged-into Comcast, I do indeed see the five folders you mention plus two more....."Deleted Items" and "Sent Items".
I'll bring this up with Comcast-Support when I make the call.
You then told me that you are in fact accessing Comcast email through the website (webmail) and not Outlook 2013. Since that's the case, and upon logging in, you also see two folders, you'll need to contact Comcast anyways. I recommend you have all devices you want configured for Comcast email available when you call, they should be able to fix your folders, walk you through setting up your email clients and making sure your Sent Items appear across all devices.
Let me write that I can access my XYL's email with either of two ways, namely----Comcast or Outlook2013.
My XYL prefers Outlook, only because she's used Outlook2003 for many years, she is familiar with it and has no interest in learning something else.
For me, I prefer Comcast because I can access my email at the family's computer or my ham-radio computer; everything is kept in just one place.
I'm aware about MS's OneDrive but, for me, that is just another layer of complexity (I like simple.)
Anyway, lets see what happens with the call to Comcast-Support and getting stuff properly set-up with the 'Sent' vs 'Sent Items', etc.
Thanks for all the input; I'll come back after the call.
73 Jerry KM3K