How to eliminate some cookies?

You posted in the wrong operating system forum. Cookies are a function of the web browser. Are you using Safari, Firefox, Chrome and what version?

E-mails should not be affected by cookies, unless you are using a webmail website for your internet provider. Most providers offer IMAP and/or POP3 e-mail support. You just need to settings for that. Sending mail with that sort of provider just requires an SMTP server for Mac OS X Mail. Note, if the juice for the internet is not coming from Telenet, but someone else you'll have to use password authentication in Mail, with a port such as 2626, 2662, or 587 with the username being your full e-mail address.

Those settings require no cookie changes in Apple's Mac OS X Mail. If your signature is accurate, Mac OS X Mail is in your Applications folder as just plain "Mail." (without quotes).