Mail Can't Open & com.apple.internetaccount process hogging 100% CPU

I managed to fix this on mine by moving the contents of the <user sir>/Library/Mail/V2 directory, but I was lucky enough to have all my email stored on Exchange/Gmail so it didn't matter about removing local copies. Seems there might be an issue with the migration of old accounts to new accounts (this also appeared in the Lion upgrade I think (https://discussions.apple.com/thread/3232542?answerId=15889369022#15889369022)

I have exactly the same issue as well! Mail will not open and it's NOT responding after a min or 2. Took up 99-100% of CPU.

Unfortunately I can't delete the local copies as those are needed.

Deleted apple.com.mail folder but doesn't change a thing.

Any other help would be appreciated!

I really don't know, I'm afraid. From reading that previous thread, it looks like there's something that causes the mail sync services to get confused with the old and new content, and as a result I suspect moving it out will allow you to get back to work, but moving it back again will likely means you're back at square one 😟

Perhaps there's a way to archive the old emails (outside of the mail app) and then re-import them after the fact?

I noticed that my Accounts.plist file in ~/Library/Mail/V2/MailData had grown to a massive 70 MB. Simply deleting this file fixed the issue (the new Accounts.plist is only 10 KB). I had to set up my Gmail accounts again, but it was a snap in Mavericks, and all of my preferences and messages are intact (since I didn't delete any of the other folders).

Strange that I don't even have ~/Library/Mail/V2/MailData or Accounts.plist on my Mac...

@Drewli77 yup that's it. When Mail opened I chose Google/Gmail and let Mail set the account up for me.

Before doing that I had noticed com.apple.internetaccounts hogging the CPU. I went into System Preferences > Internet Accounts, waited 10 minutes for the spinning ball to stop, then deleted the Google account in there. There was only one Google account in there, despite the fact that I have four Google accounts set up in Mac Mail. Anyway this one account seemed to be what was slowing down that preference pane. After deleting Accounts.plist I re-added my accounts in Mail, which added them to the Internet Accounts preference pane, but now that preference pane (and Mail) open just fine without hogging resources.

What annoys me is the fact that hitting Delete on a message sends it to Trash, which in Mavericks corresponds to Gmail's Trash, meaning it gets purged every month (regardless of the setting you choose in Mac Mail). I've been using Option-Delete to Archive it, but I wish I could just use Delete for that, since I always Archive and rarely Trash messages. I would set another folder to be used for Trash, but sadly, all of the options under Mailbox > "Use this mailbox for" are greyed out.

Like others, mail had become an unstable slug after installing Mavericks. My Accounts.plist was also huge, almost 60mb, so I decided to have a look at what was in it.

Under the <key>MailAccounts</key> section there were over 37000 instances of my partners hotmail account! - An account that has not been used for some years.

I edited the file using text edit, removed every instance of this account (by instance I mean between the <dict> and </dict> markers). When I re-saved the file it was only about 8kb. When I opened up mail, all performance problems were solved and my usual mail account & messages were untouched. The previous memory hogging "com.apple.internetaccounts" process was now only using a tiny amount of memory.

Mail is now faster than when I had Mountain Lion, and Im using a 2007 iMac.

I have no idea how the 37000 duplicate copies of a redundant hotmail account managed to propogate themselves in the xml file. Maybe they have been there for years (and may explain some of mails previous quirks?).

Tried the deletion of Accounts.plist (mine was 42mb) and it helped!! Mail is able to launch again, but have to setup my accouns from sketch. At least I can get it running now...

The problem is I have other accounts, i.e hotmail & yahoo, in my previous Mail. So how can I link the old emails storage in my MB back into Maverick?

Many thanks to nothin7 who discovered this 'trick'. ;p

Having the same problem here. Will try deleting and reinstalling accounts. If you want to backup and restore all emails, you can try email backup pro. It has been very helpful in a couple of full system reinstalls I have done in the past...

Thanks to your tip now mail works fine and is faster than ever. Quite funny I had thousands of hotmail instances too. So crazy my laptop was completely stuck just because of this hotmail/mail issue.

nothin7 thanks! I had the same problem with the configs for hotmail addresses duplicated thousands of times which makes Mavericks grind to a halt and run out of memory. It was too much to edit manually, so I had to delete the file and set up the addresses manually. Laptop finally silent now after 24 hours of fan going into overdrive while I was trying to fix the problem.

Thanks again!!!!!!!!!!!