I have read countless posts and I've tried a number of suggestions I found that may be relevant but I'm starting to throw in the towel.  Here is my situation.  I have a 2010 iMac desktop which is running Snow Leopard 10.6.8. and I have Microsoft Outlook for Mac 2011 (version 14.5.9) installed on it and use this for my work email.  Due to the nature of my work, I must have records of client emails so retaining these is very important.  My email account through GoDaddy.com was setup as a POP account. 

One day a couple of months ago, I was happily using my Outlook for Mac and it crashed.  I somehow got it to run again, but I am unable to receive emails.  When I hit Send/Receive it crashes again.  So I have just been working "offline" to be able to view old emails and just use GoDaddy's webmail online to send/receive new mail.  The weird thing is, I am able to send emails still using Outlook if I go "online," hit send, and then quickly go back offline.  I tried to backup (i.e. export) and rebuild, but it crashes every time.  I get error message 18000.  I realize this is usually a memory issue however each folder is under 2GB and I have 300GB (out of 500GB) memory available.

Due to these issues, I decided to upgrade to Office 365 through GoDaddy and installed everything on my new MacBook Air laptop.  I would really like to get my old emails off of my desktop and install the new Outlook for Mac 2016 on my desktop and begin using that.  I'm just not sure how to get my old emails and very scared about losing years worth of client emails.  Perhaps the files are just too big and it's better to keep them separate from my new Outlook?  I do use Time Capsule nightly and do have one for the night before my computer crashed.  I'm also unsure if I need to upgrade my OS to something like Yosemite.

I really appreciate any advice.  I've spent full days trying to fix this and at my wits end. Thanks all and Happy New Year!