Fetching mail locks Mail app up upon launch

Question

When I open Mail on my iPhone it locks for minutes. It is too busy fetching mail before it becomes accessible for the user. Sometimes I get a few seconds to click on a message to open, but often it goes back to this frozen status. Often I have to get to the home screen and back to 'wake it up'.
I have three POP-accounts (no IMAP) set to fetch manually. Show 50 recent messages. Preview 4 lines. Load Remote Images off.
After a while, when I leave Mail open and put the iPhone away, it becomes usable.
This is particularly annoying when sending an e-mail from another app.
What settings to change? How do you make Mail usable?

Answer 1

This could certainly be caused by a Mail plug-in. Uninstalling a plug-in may or may not be as straightforward as just removing it from the folder where it appears to have been installed. You must read the available documentation or visit the plug-in’s website to learn how to properly uninstall it (and you shouldn’t install any plug-ins that don’t include instructions for uninstalling them).
In the Finder, go to each of the following folders (if they exist). What do you see there?
/Library/InputManagers/
/Library/Mail/Bundles/
~/Library/InputManagers/
~/Library/Mail/Bundles/
To make accurately reporting this information easier, you may open /Applications/Utilities/Terminal, type the following command (you can just copy it here and paste it in Terminal), and press <Return>. You can then copy the output of that command from Terminal and paste it in your reply to this post:
ls -1 /Library/InputManagers /Library/Mail/Bundles ~/Library/InputManagers ~/Library/Mail/Bundles
Note: For those not familiarized with the ~/ notation, it refers to the user’s home folder. You can easily locate any of the folders referred to in this post by copying the folder path here, doing Go > Go to Folder in the Finder, and pasting the folder path there.