If you have Chrome Cleaner or similar installed, start by doing a registry clean-up. If your PC is getting cluttered up with old fragments of deleted files & emails, these could have clogged the system.
You don't say which operating system or email client you're using but, if it's Outlook Express with Windows XP or something earlier, this page might be helpful:
http://preview.tinyurl.com/whtvThere is also information at:
http://preview.tinyurl.com/kb9qmj5There is a free download available which claims to fix this error - see
http://preview.tinyurl.com/jw5nzgv - but, as always, be careful about what you download!
If all else fails, you may have to de-install and then re-install your email client but let's hope it doesn't come to that
Hope this helps.