Outlook email is too large, limit size to less than 20MB

Outlook 2013 Error – Message too Large – Nothing in Outboxes
This issue may occur if the IMAP folder list does not match with that of the server or if there is any large sized email on the webmail.

Check if you are able to send/receive emails on the webmail by logging into your email account from a web browser.

You may delete or move the large sized email from the webmail.

If you are able to send/receive emails normally from the webmail. Then remove the email account from Outlook and re-configure it following the section Manually setup Internet email:

http://support.microsoft.com/kb/2758902#method2

Solution 1

1. Go to Outlook and run an Advanced Find. (Click in the search box and a new menu “Search” will open – you will see the button for Search Tools and then Advanced Find).
2. In the new window “Advanced Find” – on the first line, click browse, and check all the folders (and subfolders) in the email account (You might be able to click the Search Subfolders dialog box, but it didn’t seem to work for me so I checked all the boxes). Hit OK
3. Go to the second tab “More Choices” and only click the radio box that says “Only items with one or more attachments”. Do NOT click or add anything else.
4. Click Find Now (on the right).
5. When all the emails have been displayed, sort by SIZE. You are only interested in the emails that show up with a size of 0 (ZERO!). Open the emails and you will probably see that these emails have attachments that add up to over 20MB. Delete them – and then delete them again from the trash bin.
6. Close outlook and reopen it. Run Send/Receive All Folders and it should run without the error message.

Note: You can delete from this file list and you will get the error message on every “delete”. When you delete an item from the folder, it immediately pops into the Trash folder. Just immediately delete the item again from the Trash folder. – OR – Better Yet

1. select all items which have 20MB and above, (by holding Ctrl or Ctrl+Shift).
2. hold Shift while you click on the ‘Delete’ button, it will delete it permanently.

I had six items with attachments that exceeded 20MB – mostly photo albums and architectural plans that I had emailed.

Solution 2 
It appears that emails greater than 20mb in total will generate this message.   I did this and it appears to work.
1) Work Offline (send/receive tab, click work offline, status at bottom will say offline.  you may have to restart outlook)
2) File, info, mailbox cleanup, Find items larger than 9999 kilobytes.   I Marked the ones found as unread so you can  I could refer to them.  You can flag them or move to new inbox etc.
3) search for all unread emails (or whatever) and move those to a local or archive folder that is not on the MAPI server.
4) click the work Offline and it should connect and sync with no error message.  Repeat as necessary if it does.
Note, at first I tried a search folder but that only looks for an individual attachment size not the whole size of the email. You have to do a “Cleanup” search and your limited to 9999 kilobytes.  But that will list the large emails your looking for.
Good Luck!
I’ve edited this to include these troubleshooting ideas.   This should clean up most of the folks having problems with the above procedure.
1)  You have to be offline, it does not work if you remain online.   So, make sure you work offline when moving your files (in the send receive tab you’ll see the globe with the little red x, click it and the bottom banner should say “Working Offline” )
2) Move on the local side only.  On the local side (not the post office side which I think you refer to as “Online”) move from IMAP to a local PST file (you should have an archive pst file set up on your local machine or server).   If you don’t have a local pst file,  close outlook and go into control panel, mail, data files and add one called archive or “Large Mail”. reopen outlook and move files to there.
3) If you just DELETE your large email message, remember to delete it from your trash!!!  You have to permanently delete it!  Just deleting makes it only go to your IMAP trash.  So, you then have remove the message from your trash.  This is why I suggest moving to a archive PST instead.    I would guess, 99% of those getting another message forget this detail about deleting the message.
4) Again, make sure you’ve moved all the large files off the local server in all the IMAP folders including sent, trash, outbox, drafts, etc.   When finished click the Working Offline icon again which should now let outlook sync.   The online Post Office will recognize that the message has been deleted and will delete itself.  (If you worked the process online, it will just create another copy locally)