Try this, worked for me:
1.In Finder, open your Utilities folder and double-click Keychain Access
2.Once Keychain Access loads, in the menubar, click "Keychain Access" -> "Preferences"
3.In the Preferences window, click "Certificates"
4.Change the dropdown for "Online Certificate Status Protocol (OCSP):" to "Off"
5.Change the dropdown for "Certificate Revocation List (CRL):" to "Off"
6.Close the Preferences window
7.Quit Keychain Access
8.And you're done!
Had exactly the same problem on one of my 4 mail accounts. Since one week, no way to upload past mails.
The mails of any date after the LION update display correctly, but none of the mails before.
Strangely, the other mail accounts do display (most of) the mails contained, but some older ones not: there is no pattern as to which date the cut-off is - it is different for each account. The entire Macbook was re-indexed (with Spotlight) after the LION installation, so the searching Dot within the spotlight lense no longer appears.
Major bug from a user perspective, as effectively all previous mails become inaccessible.
Any other users with similar problem?
I tried the solution proposed by DoctorDee - very well explained, was easy to do. I did subsequently close mail and restart the Macbook. However, it did not solve the problem,
Found a solution at last... After over 2 weeks trying to get stuff working again so I could do my business — my printer, my scanner, my 3G modem and several apps for starters (plus some games and utilities) — I've uninstalled Lion completely and reverted to Snow Leopard. It took almost a day to execute fully but the saving in stress and frustration has been well worth the time and effort.
The only problem I found in the process was after starting from the original SL install disk, when it searched for available drives it refused to allow my MBP's HD saying SL could not be installed on it (it didn't mention any conflict with Lion so that's probably not why). I had to wipe the HD first using Disk Utility on the install disk, then run the install, then update using the 10.6.8 Combo Updater, then run Software Update, then Migration Assistant to bring in accounts from my backup (a Carbon Copy Cloner clone), then transfer all files from my original Home account on my backup into the Home accout on the new SL installation. Done.
I'll wait till next year to try Lion again, or at least wait until I have the time to research all the possible feature/app failures related to installing Lion so it won't block my workflow.
Some solution... but it has been 100% successful.
I've had EXACTLY the same problem on my 2010 MacBook Air which I upgraded to Lion a couple of days after Lion came out.
The laptop is used as a companion machine to my main Mac Pro and as such I had the 2 POP3 accounts which are on it configured to not delete messages from the server.
As I had all the old e-mails on my Mac Pro (which I've kept on Snow Leopard for fear of losing access to my existing e-mails) I simply deleted all the existing e-mails on the MacBook Air. I realise this solution won't be suitable for everybody!
All new e-mails arrive fine.
Today I have been contacted by a colleague who has recently updated their MacBook to Lion and experienced EXACTLY the same issue. Unfortunately in their case, they have no other machine with the e-mails on so are now completely unable to access existing e-mails, instead they just get the "Loading..." message (exactly as shown above). My colleague uses POP3 accounts but does not have them configured to leave the messages on the server.
This is a serious issue - is there a reason for it or a real solution (reverting to Snow Leopard as mentioned above doesn't fix this issue, it just overcomes it by ignoring it).
If DocterDee's solution is effective - can you please explain why this is so?
I understand you saying reverting to SL is not a real solution to this problem. But to me it was a real solution in that I was experiencing myriad other problems besides the Mail one as a result of installing Lion and ALL were eliminated for me with my 'solution' which enabled me to run my business again without having to spend further hours and hours (in Windoze-like fashion) sorting out so many operational issues that were not just petty ones but business-crippling ones for me.
I actually upgraded too early to Lion, but I've always upgraded to every major new OSX release straight away and any problems have always been minor and were overcome fairly quickly and easily. This one is just un-Apple and a total time-wasting, money-costing (other than the Lion purchase price) hassle for me; an expensive time consuming trap I will be wary of in future.